When Randall is selling the 4 year old girl cigarettes, the sign on the register which says "If you plan to shoplift, please let us know.", mysteriously disappears for one scene, then reappears.
Knowing the general attitude and humor of Kevin Smith, he probably did this as a joke. If you've ever watched any of the commentaries he does, you can notice his "other" sense of humor. One which is very subtle. He does the whole "potty humor" throughout his movies with the excessive swearing, gay jokes etc. But he also has a hidden sense of humor that likes to play little tricks like that.
I believe that I can partly agree with *relish*.....if you listen to Kevin Smith out of character (like you could really "listen" to him in character), but if he is just shooting bull then you can tell he is the type of guy that loves to toy with people brains...keep them on their toes....it's part of what makes him the best writer/director ever.
Actually if you get the clerks dvd, kevin smith says that they only realized about the sign after watching the completed movie. They didn't do it on purpose