They sponsor people who they think will help them sell product and make money. Not enough people care about the tattoo to complain about a sponsorship.
Obviously. Nike Mexico, then. Or Affliction, Tecate beer .. whatever, but it won't be a mass general sponsorship like the ones given to Bones or Anderson.
Now that Cain is champion again, he would be a good choice for Nike to sponsor. He could probably get Nike Cortez to fly off the shelves like they did in the 90s.