[EricH]

Originally Posted by Kingland093

My team has used it on the outside of our bumpers and the refs never said anything about it

A couple of comments on this:

1) Duct tape (or gaffers' tape) is legal, for repairs at least.
2) If you're using it for numbers, and the numbers come off, someone really needs to talk to you--risk of non-compliance with G26.
3) If you had it at inspection, the inspectors, NOT the refs, could have told you whether or not it was illegal. (Just ask--most inspectors won't bite you for asking if something is or is not illegal.)
4) Just because the refs don't say anything doesn't mean it's legal. It may in fact mean that they don't care about that particular infraction, if there is one. But at your next event, the refs might have a little more time to care... and now you're not legal.