Remember when I made the Planet Tamer badge for people to use? Link: Cabot's Planet Tamer Badge - Re-Created + Monster Badge
Well a streamer on Twitch is using the same exact one I made (but edited slightly) and is using it for his merchandise, such as t-shirts which can be seen here: http://imgur.com/CKJub6K
I edited out his name to avoid any flaming. I had no intention of using the artwork for financial gain since the design was mostly based off of Turtle Rock Studios, and I assume if I wanted to utilize it for business use I would need to ask permission of some sort.
Any advice on how to deal with this?
Edit: Forgot to provide link to the store image