So make a transaction from somewhere else, paying dust to the paper wallet and including an OP_RETURN output. Or top up the paper wallet with dust then spend that dust making an OP_RETURN output. Anyone looking up the address will notice something going on without invalidating the original output.
THIS is an excellent approach! But as OP wasn't involved with Bitcoin before, unfortunately unlikely to happen. Transfering a little dust to the paperwallet's address together with a commentary OP_RETURN should cost less than ~1000sat (I'm too lazy to figure out the cheapest amount). Removal of dust would need to be done by the finder himself (don't trust others with the private key!).