I bought mine the same way, but I don't think the S means it's a second.
These knives were shipped from Mikhail inside the US (at least mine was). It appeared that it was shipped from a warehouse in IL to Mikhail, who then mailed it (envelope inside of envelope). I had guessed that the "S" was for "SSE" and a quick way to determine the contents. Anyway, it looks like a very sharp sharpie, it would probably come off if it bugged the new owner. I really don't even notice it - and was happy to have it since they were charging $10 extra for the pouch during their sale! All my other CKF knives shipped from Russia.