Early wireless royalties

The B.B.C. Stamp & Post Office Registration Scheme

"In Britain, the BBC was instrumental in the 'roll-out' of commercial wireless during the 1920s. During those early days of broadcasting the BBC raised a large part of its revenue from royalties arising from the mandatory application of the BBC stamp to commercially produced wireless sets and wireless 'accessories'."

Via my Dad, whose latest crystal sets bear the mandatory manufactured-and-approved-in-Britain seal.