I don't remember seeing this board on the set, and none of the boards in the movie had a Liddle label on them in addition to the Bear label...although Greg built some of the Bear boards they used.
It may well have been one of John Milius' personal boards. He got a couple from Greg back then, as working on Big Wednesday rekindled his interest in surfing. (John, by the way, was a pretty good surfer.)
This is George in El Savador during the second unit filming of BW. That's me with the Liddle T-shirt behind him.