Now that you mention that I remember seeing 'Batch Process' in one of the programs that came with the camera. So I checked and I found it but this is the options it gives me:
I don't see anything in there that lets me 'sign' my pictures but maybe I'm just missing it (very possible lol).
No, you're not missing it.. your software doesn't offer it. It's not that common of a request, as those who normally watermark their pictures are professionals.. and I would imagine that most, if not all, professionals use non-free software for their volume processing.
Like I said, Photoshop Elements offers it, but it'll run you $100 or so. ( Well worth it, in my humble opinion )
Another thing would be to do a google search on 'watermark' 'photo' 'free' and see what pops up.
Good luck!