DAVID GREENE, HOST:

Good morning. I'm David Greene.

(SOUNDBITE OF SONG, "MAN IN BLACK")

JOHNNY CASH: (Singing) Well, you wonder why I always dress in black.

GREENE: In 1979, Johnny Cash added a little blue to his attire. OK, not actually, but Cash did have the authority to enforce the law in Davidson County, Tenn. A blown-up image of Johnny Cash's deputy sheriff commission card was unveiled earlier this week at the Johnny Cash Museum. Got to imagine getting pulled over in Davidson County and Johnny Cash telling you to walk the line. Transcript provided by NPR, Copyright NPR.