DeviantArt is pretty shoddy when it comes to dealing with art theft from what I've been able to gather from other users. Recently this bloke - kman1415.deviantart.com/ - has done the same to me which...doesn't hassle me so much as bug me.
Pretty much all I'll be putting on here these days are Manga colourings that I occasionally get requested. Even so I can figure why people who're really talented artists and get their stuff stolen get so irate (and hurt) by it.
And DA is pathetically slow at resolving these issues. Seemingly especially if you don't pay them anything. I could be wrong, but in my experience and with what others have said...they're pretty bad at it.
This is why despite my reservations I've stuck those blasted watermarks on there. I don't accept credit for the original image (done by the actual Manga artists themselves), only the work I did myself to lend them colour and I make a point of specifying that fact. Even so it's not nice to basically swipe even that with no credit to the contributor.
Since I'm ridiculously slow at making these vector images anyone reading this should hang in there and wait and see what I can motivate myself to do.