Well, Deviantart has a mature filter you can turn on/off, but sadly not all artists will bother with that. Usually if you just stay safe, keep the maturity filter on, and usually not go near the 'newest' page or 'popular' page, you'd be safe. I honestly don't know any art-sharing websites besides Deviantart, so I'm not too much help lawl
Just keep in mind that everybody's definition of 'art' varies, and I don't believe in 'bad art' myself, even if I don't prefer looking at certain things. So, some art sites will probably allow a lot of things with mature content, and you'll have to respect that.
If you want completely safe art sharing sites, I'd honestly look up art sites for kids, since they will probably be much stricter with their art. I know that Chickensmoothie has an art program, but you can't upload art that you have previously made with other programs.