A happy worker with his hard hat... From another world or time... :-)
This sign holder was working for California Proposition 14, a ballot initiative which gave farm workers the right to unionize. In California, laws can be created or repealed directly by the voters and bypassing the elected legislature. The initiative process allows the voters, (given they collect sufficient signatures), to approve laws via statewide voting ... direct democracy. Prop 14 was one of those direct democracy actions which passed. The promoter of farm worker's rights was a gentleman named Cesar Chavez, who is a bit of a folk hero in certain circles.