Often, men just don't notice these things. Also, this will also depend on how you present yourself. For me, having a pimp (like someone suggested above) is laughable. NO ONE would even think that this would happen with me.
So if they saw bruises on my butt, they might not appreciate it, but then again, I'm VERY fair skinned and I bruise easily. Also, well ... sadly or gladly, I'm Elisabeth and I'm painfully honest and fairly bold with my clients. If they've seen me before, probably very little would surprise them.
But what I first thought, is unless it's rather bad, men just aren't going to notice it. Just tell them. Chances are good that it's not going to be a big deal either way.
Hugs,
Elisabeth
P.S. Just to add another thought as a result of seeing the above post. Krunkman is right. I've been bruised before and actually the few men that saw it were turned on or they asked me about it. Really, not a biggie unless they're the sensitive sort. And men are easily redirected. Just lead them astray. Isn't that the fun part anyway?