Hermes has their leather products stamped with a Alphabet to represent the manufacturing year since 1964. The date stamp is one of the ways to authenticate a Hermes, but it is however not difficult to fake for the copy bags makers. So a Hermes with stamp does not mean it is real. On the other way, a Hermes without a stamp might not be a fake one (but probably is). It is possible the stamp was not crafted deep enough by the crafter and simply faded out as time passed.  

Anyway, It does not do you any harm if you can understand the stamps on Hermes! Check out the table below to find out which year your Hermes manufactured was! 

Stamp S is skipped because Hermes does not want their products with stamp S to be confused with the discounted products (Hermes holds warehouse sales for the most royal customers regularly, and the products sold there would be stamped with a "S")