French 1860 12 Red Mark On Cover

The 12 mark is not common. I searched auction catalogue and other sources and could not find reference. Please help

Was this taxing a short paid letter? I'm just driving by during the workday, and can look more tonight.

The 12c is credit towards the Arago steamer.
auction example:

It seems that someone has already found an answer.... :)
My message has no sense anymore.

I checked in Yvert Tellier 2022. Napoleon 80 c carmin has no special number cancellation as in your letter.
There are a lot of cancelation on http://marcophilie.org/x/y-an-3.html but nothing with red numbers. You can continue your search on Marcophilie site, maybe I missed something.

My last search was in the book "The use of postal history in thematic" by Dominique Hardy.
There were some red numbers used on what is called The "Petites Postes" but I am not sure if they were still in use in 1860 or in Le Havre. Your letter has a cancelation with "Bureau maritime" so in the same book I checked the examples presented for the moving boxes boat (Le service boîte mobile bateaux) but there are no red numbers.
My suggestion is that 12 refers to a special post office/box.
You find in the photo an example with the Petites Postes.

racines, the reason why the Y&T catalog does not show "12" as cancel is because the marking was never intended to be struck on a stamp but a cover itself. The OP's cover is not an example of a postal clerk with bad aim.

Secondly, you refer to markings used in the 1790s. I believe the table you scanned shows the earliest known dates and the last known dates of use. Does it? You will have to prove that they were still being used some 65-75 years later.

12c for a ride across the ocean on this thing?



"Yeah, no. I'll wait for the next one, please."

The Arago was commandeered by the Union government during the U.S. Civil War. It was used to return the U.S. flag to Fort Sumter in 1865, restarted mail service, and was eventually sold to Peru in 1869.

In the light of the following document

https://siegelauctions.com/ph/pdf/022.pdf

I agree with the previous posts, 12 must be a sort of charge/tax.

Thank you very much for the helpful discussion.
I have several 80 centimes letter I'll post latter.