The mystery of the “C-C” on my 1927 500-peseta banknote: three hypotheses on an embossed stamp that baffles experts

Anyone who collects banknotes knows that each piece tells a story. But sometimes, a small detail presents you with a real mystery. This happened to me with a 500 peseta note from 1927 (Isabel la Católica, issued July 24). The banknote has the usual Republican dry seal from 1931... but between the coat of arms and the crown, instead of numbers, there are two clear letters: C-C.

These are not initials that appear in standard catalogs. And since I discovered it, I haven't stopped asking questions. The best part has been the generosity of two great experts. Each has given me a different hypothesis. And here I want to share them, thank them, and, above all, ask for help to continue researching.

But first, a small theoretical basis to help us understand.

What is a hypothesis and why do we need several?

A hypothesis is a provisional and reasonable explanation for a fact that we do not yet fully understand. It is not a closed truth, but a starting point for further investigation. In numismatics, hypotheses allow us to make sense of marks, overstamps, or variants that do not fit into what has already been described.

And in this case, confronted with undocumented C-C initials, three hypotheses compete (and complement each other). I have ordered them as follows:

1. The "Quality Control" hypothesis (as a testing stamp).
2. The "worn 6-6" hypothesis (defended by an expert after seeing my photos).
3. The Central Council / Control Commission hypothesis (suggested by historical documents and AIs).

Let's approach each one with the care and rigor they deserve.

 Hypothesis 1 – Quality Control: a test stamp in 1931?

This was my first idea after reading several forums and online information. I thought, "What if C-C meant 'Quality Control'?" Something like a stamp used by press operators to verify that the die was stamping correctly before moving on to good banknotes.

Why could it be?

• It is common in industrial processes for test markers to be used.
• The location (between the coat of arms and the crown) seems like a "secondary" space that does not interfere with the main inscription.

Why am I doubtful?

• In 1931, there was no "quality department" as there is today.
• As far as I know, there is no documentation mentioning such use in Republican dry seals.
• And most importantly: if it was a test, why would it have ended up on a banknote issued to the public?

Although I find this to be the weakest hypothesis, I'm keeping it open. Just in case anyone has seen something similar on other banknotes or stamps from that era.

Hypothesis 2 – The wear and tear of time: they are two "6-6" that now look like "C-C"

Ramón Cobo Huici, after carefully examining my photographs and comparing them with his extensive collection of Republican dry seals, gave me his opinion. And he didn't beat around the bush. He told me, verbatim:

"You are starting from a visual error.
*The dry seal consists of the Spanish coat of arms, surrounded by a laurel wreath and crowned with a mural crown. Between the coat of arms and the crown, there is always a pair of numbers separated by a hyphen (X - X). The most common pair is 4 - 8, and some catalogs state this, but about two years ago, Castellanos started asking everyone, and about 8 different pairs appeared; the meaning or reason for this numbering is unknown.*
The stamping presses, I'm sending you their image, I took it from a newspaper of the time, they were commissioned by the Bank of Spain because, according to the ministerial order, only the Bank of Spain offices could do the stamping, and I recall there were about 50 of them.
We start from the premise that Asturias was never isolated in the early years of the Republic, and a branch of the Bank of Spain could not have made a matrix at its whim.

In my banknotes, I used to see a C or a G, until I realized they were 6s. Since the numbers are so small, there are cases where the circle of the 6, when printed, is filled in, other times it is empty (a C), other times it is half-filled (a G), and other times it is completely unclosed (a C), and that is what has confused you.”

His hypothesis is clear and technically very consistent:

• Republican dry seals always carry numbers (not letters) between the coat of arms and the crown.
• The most common number is 4-8, but there are at least eight different numerical variants, the meaning of which is still unknown.
• What I see as two Cs are nothing more than two sixes that, due to the tiny size of the die and imperfections in the stamping, have been left with the upper circle open (like a C) or half-closed (like a G).
• Furthermore, the Bank of Spain strictly controlled the stamping: only its offices had authorized dies, and in 1931, Asturias was not isolated, so a stamp with different letters would hardly have been made there.

But Jaime Sanz, another scholar with a clinical eye, openly disagrees after seeing my photos:

"I have handled dozens of Republican stamps and have never seen sixes turn into such clear C-Cs. Furthermore, the curves of the C are very different from those of a 6, even if worn or poorly stamped."

And here I am, with the banknote in my hand, seeing two perfectly legible capital Cs. I'm not saying Ramón is wrong—he has seen thousands of specimens, and his explanation of the presses and numbers is impeccable—but the current shape still seems to me, I insist, two letters. Perhaps a hundred years of wear and a defective factory stamping have created this convincing optical illusion.

I am deeply grateful to Ramón for taking the time and sharing his knowledge with so many technical details (the presses, the numbers, the ministerial order). And to Jaime for maintaining the discrepancy. This kind of healthy debate is what drives numismatics.

(See update at the end of the post)

Hypothesis 3 – The Central Council / Control Commission (Asturias-León, 1936-37)

This third avenue was first pointed out to me by artificial intelligence after I uploaded photos of the banknote.

What does this hypothesis say?
That those C-Cs have nothing to do with 1931, but with the Civil War (1936-1937), in the so-called Northern Front. There, the Sovereign Council of Asturias and León overstamped Bank of Spain banknotes with its own dry seal to give them local validity and curb the "stained paper" of the Nationalist side.

The acronym C-C would mean:

• Central Council (highest political authority)
• Control Commission (operational body that physically stamped the seals)

This hypothesis is supported by documentation: Official Gazettes of the Council, decrees from 1937, and similar examples in safe-conduct passes and rationing vouchers. Additionally, some catalogs mention local overprints from the north, though without always detailing the C-C.

The good news: It explains why the seal is dry (same technique as the Republican one), is in a similar position, and appears on a 1927 low-series banknote (very common in the northern area during the war).
What's missing: A photograph or explicit reference in a main catalog stating "C-C = Council of Asturias". For now, it's a strong but not 100% proven hypothesis.

Update May 9, 2026 – New data provided by experts

Recently, after the publication of this article, the prestigious specialist Ramón Cobo Huici has confirmed owning a specimen with the same characteristics in the central area of the seal (apparent acronyms "C-C") which he has had since 1992. "I had sent all the photos of my banknotes with dry seals to Castellanos some time ago for his study and I didn't know I had one! What a joy!" It is important to note that the interpretation of the acronyms in the center of the dry seal can vary significantly depending on the lighting, the angle of the photograph, and the state of preservation of the relief. The numbers "6" engraved in dry relief, after almost 90 years of circulation and manipulation, tend to lose their open top and become rounded, adopting a shape very similar to the letter "C," which is why this debate arose and is slowly being clarified. And... here is Ramón's C-C seal:

According to his communication, the renowned researcher José Antonio Castellanos —author of the most complete encyclopedia of Spanish notaphily and an expert in Republican dry seals— has collected and studied a total of four specimens with this peculiarity (including the current banknote and Ramón Cobo's), which I show you below:

Castellanos, who for years has been requesting images of dry seals from numerous collectors to conduct a systematic comparative study of die variants, is analyzing these cases. Below we show you the other 2 known specimens provided by Castellanos through Ramón Cobo:

 My stance: none are closed, all are necessary

As of today, I don't have a definitive answer. What is clear is that my 500 peseta banknote from 1927 is, at the very least, special. And it's not worth a fortune for that reason—its conservation and number of folds will always be the most important factors—but it does have a unique story that begged to be told.

If you have a Republican banknote with a dry seal and letters appear between the shield and crown, please write to me.
If you have seen other C-C marks on Alfonso XIII 25, 50, 100 or 1000 peseta banknotes, I would love to know.
If you know of archival documentation (Bulletin of the Council of Asturias, minutes, bank circulars, documents from the period) that expressly mentions these acronyms, please share it.

And, of course, my huge thanks to:

• Ramon Cobo Huici (for his honesty and help in clarifying this mystery a bit).
• Jaime Sanz (for his reasoned disagreement and keen eye).
• Castellanos (for his contributions and studies in this field over the years).
• And to the AI which, without being an expert in notaphily, pointed me towards the Sovereign Council without me having asked.

Together we will continue to unravel this great little mystery.

This blog is intended for the community of collectors, and we learn together every day. If you find any errors or wish to contribute additional information, please email us. We will review your contribution and update the content if appropriate. Thank you for being part of this community.