I'm pretty sure I remember a contestant from last year who made it on-stage with a shirt that referenced some organization. I guess they thought it wasn't a problem at the time, but apparently something must have come up by the time they aired it as the decision was made to blur out whatever was on the contestant's shirt and the shirts of all the people in the group. They slipped up once during the Showcase Showdown and the group's name was visible for a bit. I remember searching it up but, for the life of me, I can't remember what the group did.
EDIT: Quick search over at Golden-Road reveals that it was a group of people wearing a shirt advertising a rapper. Also, apparently, they (the show) figured it would be a problem before the SCSD and by that time the contestant's shirt was covered with black tape.