The best way to do it would to etch the school name and a number on the back in the name space (assuming you're using TI83 or 84s which have them) and then have the numbers assigned to teachers. The best way to do that is with an etching tool, which your shop department might have, or there's the PITA way using a pin. My personal TI83 has my name etched. The other more permanent way to do it is to use an older labeler, the kind that produces raised lettering. Those things stick like none other. I have old labels that have been on for 25+ years. Residual sharpie will come off with rubbing alcohol.