Happened just this morning.I hadn't even noticed. Took a bunch of mailers in to weigh and pay. The clerk (not the cute one ) said, "did you put this stamp on here?" (All the others were blank or had metered postage affixed.) I said, "no." She said,"you want to use it?" I said,"I hear it,s a federal offense to use it." She shrugged her sholders and threw it on the pile with the others. Didn't charge me.

My suggestion might be to hand it to them, play dumb (in my case, I wasn't PLAYING dumb ) and let them decide.

Later.....Rick