OP I have been watching Adult Swim since it's debut in 2001 I believe, and I will tell you with NO LIE (although also no proof) that for a brief time around 2002 or 2003, the owl was the mascot of Adult Swim. It was featured on many commercials (actually called bumpers, they are technically part of the presentation and not REAL commercials) and the owl was treated like a character or mascot, as I said.

It may be possible to find more information about this online, I don't know as I haven't looked into it or watched Adult Swim for many months.