We nearly put out a batch .040 metal signs because they had a clear liner on one side of them unlike the pink or blue liner we typically get. Only realized it as they were at the front counter for pick up and someone noticed a corner lifting. Everything gets a liner check now! We'll write on clear liners so that an installer doesn't forget to take it off on the jobsite, but I remember one case where the customer called us the next morning saying their backlit sign was vandalized at night because they could see large Xs. Next day the installer went back out and didn't see anything so he came back. It wasn't till I asked him if he took the liner off that he realized he didn't.