We have been wrong to think that part 15 radio stations are unlicensed. It's all in word definitions.
License as a verb means "give permission." Part 15 of the FCC Rules gives permission to OPERATE... another key word:
Operate is a verb meaning "to function." Look at the word's appearance in 15.219:
15.219 OPERATION in the band 510-1705 kHz.
That single line grants PERMISSION to FUNCTION in the AM medium wave band, in other words it grants LICENSE to function.
For those who think a license is a piece of paper we point to the word LICENSE as a noun... which refers to the permission we have as well as a document recording that permission.
The Part 15 Rules themselves are a document recording our permission to operate, and so stand as a valid license IN THEMSELVES.
At the same time there is no prohibition against expressing key portions of the part 15 permission on a self-styled document suitable for framing and hanging with signature and seal.
Government publications and symbols are in the public domain and as long as truly reflecting the contents of part 15 can be employed to form a legal and proper document.
This point of view is beyond refutation.