They're mildly obscure. As in you would almost never see someone wearing a shirt at school or in public, but you will see some at shows.
Back to the topic, I don't know where you would find info, somebody posted about concert figures a while back, which would also be interesting. Maybe record companies don't want the figures out unless they go gold/platinum?
4/11 Fear FestEvil w/ High on Fire
4/17 Electric Fucking Wizard
4/28 Mastodong/Clutch/Big Biz