My wife was staring at my weezer shirt (the T-shirt version of this: http://weezer.cinderblock.com/make-believe-onesie-blue.html) today, and asked if the band members got to pick their characters on the shirt. It made me wonder, how much of a roll does the band play in their merchandise design?
I don't think the band usually get too involved outside of just approving things. Sometimes they may contact an artist or something that they want to make a design for a shirt, or sometimes they may have those ideas brought to them by management or a label or something for approval (or a fan may give them an idea).
Once in awhile they may come up with something on their own and make it happen though. I'm sure that's happened before, especially in the earlier days.