I don't know how formal your wedding is, but what about something like this? It doesn't quite have the S&M connotations.
Oooh..I like that one..I dont think the SM is going to have that "head in the gutter" effect as much as if you used the &. I really had no choice in order..As our initials are both S. Even worse the last initial is S too. So we could do SS..S&S..or SSS...Although I never thought until now that We probably could've just got away with a single S..lol..Oh well.