Hi there! New to these boards, but I thought I knew the source of this picture, and as the wikia page says
- There is art of Sigma with one hand behind his head that has existed since the game's release, but it is unknown if it is actually official or fanart as no official source has been given.
Using saucenao.com, it showed me that yes, the source for the picture is by a user called B O S made back in October 6th, 2012. Anyway sorry if this has been discussed or brought up before~