I don't know for sure, but I read on this forum that the serial numbers that begin with P or S are the later frames with the beefed up stays that are not prone to cracking - as opposed to the earlier enduros. I don't know what those serial numbers begin with.
no, its not near the ser.#, its just by itself a simple capital S, the reason I'm asking is that its supposed to be a med. frame, if anyone who has a 05 enduro would look at theirs and see if maybe Larges have an L etc. or could it be for Sworks?
I also have a Med 05 enduro pro and it also has an S stamped. It is not the frame size thats for sure. there is also a sticker badge on the frame saying where its made and what size etc. If you really have doubts about what size your frame is, measure it and compare to the specs on the specialized site to alleve your worries.