'Stone Cold' was starting to gain momentum in 1996 thanks to his 'Austin 3:16' catchphrase, and Vince McMahon wanted to cash in by putting the slogan on some merch. When Austin suggested that they put a big old skull on the back, Vince hesitated.
He told Steve that he'd need to run that one by 'Taker first - skulls seemed to be part of his macabre gimmick and the boss didn't want to tread on any toes.
Austin remembers strolling up to 'The Deadman' and asking for permission. The Undertaker didn't have a problem with it, but appreciated Steve asking his opinion; 'Taker probably realised that his peer was only trying to get ahead and make some extra money.
It's a good thing too, because the skull motif went on to become a huge part of Austin's act. He's still using it today with ventures like his 'Broken Skull Sessions' show on WWE Network.
None of that would've been possible without 'Taker's say so.