Per Internet:  The Disabled American Veterans (DAV) purchased the ident-o-tag company in 1941. License plate keychain tags were used since 1938. The New York based “Lost Key Services” was among the first. There were other advertising tags used too, but you had to order the tags. The DAV was able to get the various state motor vehicle departments to co-operate with them and give them the mailing lists of the people who registered their cars. The DAV mailed tags with your license plate number on them and asked for a donation. The premise was that if you lost your keys, the finder would drop them into a mail box, and the DAV would return them to you. The program continued from 1941 through 1975, and was ended because of a “right to privacy rule”.