I stumbled upon this user who had this ¿pornographic? gravatar,

(Note that the Gravatar rating system seems to have failed in this case.)

While I, personally, think that such pictures are swell and would love to see them be allowed, my guess is that Stack Exchange sites want to maintain a more "family friendly" image? But I don't see a way to flag user profiles or gravatars.

So, appropriate action when such profiles are spotted?
Time to sue Gravatar back to the punch-card era?

Update:

The user's profile avatar has been changed from 07ded368f8cbe358ce04c259a3cd8236 to 012bd5f0815be2480925059b17be8376 by a moderator.