It's not strictly illegal, although I'm not sure on the ins and outs of it. If the band didn't want their tee featured in the video, and the video is used for commercial purposes or even displayed publicly, then they could go through to motions to have it removed. I believe they could also try and push for some sort of compensation/royalty payment, but it would be a long shot for something as simple as a tee shirt in a music video, they would have to show that their image/logo/brand was being used for commercial gain etc. It also starts to get messy when you're dealing with internet publishing and international law..
If the logo etc. is used in any sort of defamatory context they could also have it removed etc.
But yeah, for the most part when it comes to music videos, it's more of a case of the band members giving a shout out to their influences or inspirations, that sort of thing.
When it comes to advertising and more commercial purposes, measures are taken to prevent any sort of unauthorised logo or anything from being featured in the clip. When I worked as a trainee for an advertising company, one of my main jobs with film productions was to take a roll of duct-tape and cover any logos, branding, etc. to prevent it from causing problems down the track.
Originally Posted by Stigs
I could never get past anything involving exponents, atheists don't believe in higher powers.