This weeks episode of The Flash "Welcome to Earth 2" was full of DCU Easter eggs and even included a cameo from Supergirl.
The Legion ring made an appearance while the team was traveling to Earth 2.
Aside from Supergirl another face made an appearance. This one however was wearing a familiar green hood and costume.
Now this could very well be Connor Hawke who's set to appear on Legends of Tomorrow but he seems to have a familiar looking face. From this image the man looks like Andy Diggle. Well it could be Diggle in the costume but the figure appears to be smaller (in body size I think) than Diggle, could it be his brother?
Ubove is an image of the actor who plays Andy on arrow and if you compare the two the facial features look very similar. This being him would also make a bit of sense as they've been building up his character on Arrow.