I use to eat lunch with Phil Lesh when he was in town, we would drive on weekdays to the Trident from San Rafael in his car for a legit reason to drive somewhere FURTHER than Marin Joes.    If I remember correctly, Kelly had something to do with the tee-shirt design. I don't remember buying it, but I do remember having a Trident shirt.  David Crosby talks about the Trident and his sailboat in his first book. 

 

Photo and post courtesy of Tom Smith 

(Photo taken at Giant Stadium in 1978)