PHJim: "Elvis used mailbox letters to put his name on a Martin dreadnought (the famous "Elvi" guitar). "
Stevie Ray Vaughan supposedly got his glitter "SRV" at a Texas truck stop.

I think bass drums have always been a billboard:
http://www.goreadingberks.com/articles/images/johnphillipsousa/stcyrilboysbandlarge.jpg

For a century or so the circus calliope was a musical instrument with the sole purpose of self-promotion. You could hear some of the big "named" steam powered beasties 3-4 miles away:
http://farm3.staticflickr.com/2729/4451411291_d43bdab2c8_z.jpg

(For some reason I can't make a "blue clicky" out of those.)