That is true that one does not NEED to have a license. OSHA only requires proof of satisfactory training to be kept by the employer. However, many employees feel as though they should have something to indicate their authorization to operate powered industrials trucks.
Here at Micros, we all have to carry electronic identification / key cards to gain entrance into the building. We normally have them in plastic sleeves with an alligator type clip for attaching it to your belt or pants pocket or a retractable device on the belt. The cards I designed are credit card sized and fit very nicely in the back of the employee magnetic ID cards. In this way, each operator would have "proof" of training should an OSHA inspector pop in one day.