One difference I can see is that if someone tries entering an ID of something they've found to check the reward, it notifies the owner automatically. Someone wh

One difference I can see is that if someone tries entering an ID of something they've found to check the reward, it notifies the owner automatically. Someone who's 'found' a wallet or phone might want to check the reward amount, and then feel obligated to follow through with returning it once they realize the owner has already been notified. This contrasts with a contact number, as the person in possession of said item might decide they'd rather keep it than phone the owner when the reward is unspecified.