Here's the pertinent material from the guidelines:
"We expect the images to be R-rated or milder, meaning no explicit genitalia pix or overt sexual behavior depicted. We also expect the images to be respectful of others, meaning no bigoted or derogatory slogans or portrayals."
Explicit genitalia pix are right out, so please flag them. The term "explicit" covers shots that focus solely on the genitalia or emphasize the genitalia, among other things. Simply seeing bits as part of a larger picture isn't necessarily going to violate the standard. Any sexual activity is also in violation, such as masturbatory touching in the image.
While this is an adult site, it is not a meat market nor a sex site nor should it ever appear to be.
Now, I've not been paying attention to avatars and certainly not scrutinizing those of newcomers as they join. Is this something I need to begin paying attention to? Are enough avatars not following the guidelines appearing that I need to begin actively looking for violations?
When speaking of various forms of non-monogamy...it ain't poly if you're just fucking around.
While polyamory, open relationships, and swinging are all distinctly different approaches to non-monogamy, they are not mutually exlusive. Folks can, and some do, engage in more than one of them at a time--and it's all good.