Let me tell you a thing, it ain't cool to steal people's art! Don't do it!! And if you post an art-piece that isn't your on a social media site that isn't dA, make sure you source and credit properly! It's extremely insulting when someone has so little respect for my work and stuff that they save it, edit out my signature, and upload it as their own.
If you do see art that doesn't seem like it fits into someone's portfolio or you see something that seems off about it, do a Google image search and see if you can find the original uploader, and then let them know! I am extremely grateful whenever people let me know when they see my art stolen.