Before I took Buttercup to get him neutered he didn't have anything on his inner thighs. After he got neutered and when I picked him up (which was May 11 of this year) I noticed something on his left (or right

) inner thigh. I didn't think much of it at first. I just thought that it would go away after 2-3 baths. It has now been over a month and that 'thing' is still there. Could it be a tatoo? If it is, I never asked or gave them permission to do it. Here are some pictures of it. I tried the best I could. Sorry for exposing a little too much.
Should I call his vet and mention this to him? I don't think I like it very much. He didn't do a very good job on this tatoo (if it is one)