A good book on sex magick i found was Modern Sex Magic by Donald Kraig. Actuall as I look at it now it even has a section towards the back invovling bdsn practices in sex magick. It talks alot about symbols and talismins in some of the early chapters though.

I almost alway boil my magick down the the simplist form. I find lots of complications to distract me so rather than symbols i choose a word that represents what it is I want to achieve and focus my brain on that. So far I have had great success with sex magick. I haven't really tried it with bdsm yet, but I am interested in mixing teh two.

One way I would use symbol in a sex magick ritual would be inscribing the symbol(s) on teh body of the sub, using him or her as a focus. I actually am hoping to try somethings wiht my Lord soon, so I will keep you updated as to what happens.