The below link shows the first page of a Frank Zappa & The Mothers of Invention contract signed by the entire lineup of the 9 man Mothers.
It's a 7 page agreement for the Mothers' appearance on the Steve Allen Show (where Zappa previously appeared, a few years earlier, playing a bicycle !)
Signers of this contract are Frank Zappa, Ian Underwood, Roy Estrada, Bunk Gardner, Jimmy Carl Black, Ray Collins, Don Preston, Euclid James (Motorhead) Sherwood, and Artie Tripp.
This came from the archives of original Mothers manager Herb Cohen, and is / was offered for sale on ebay.
I've added the picture to the U.M. pages (FZ > Oddities).
And I've also added a picture of the 1966 American Federation of Television/Radio Artists union agreement for Captain Beefheart over at the "CB > Weird Stuff" entry
-- thanks to Brainpang for the info