Sorry I couldn't find any information about this one, but key return tags of the same style were fairly common around 70-90 years ago. (Alpert & Elman suggest a date range of 1920's or later.) Some were issued by registry companies, others by insurance companies, banks, or various advertisers. Supposedly, the issuer maintained records which would permit return of keys or other property to the owner (or identification of the owner himself in case of death or serious injury) by means of an identification number stamped on the tag or fob. In some cases this would also be his insurance policy number, bank account number, or the serial number of an item which he had purchased from the company.