Armand Hammer, Arnie's great-grandfather, was the oil mogul.
Armand's father Julius was involved in forming the Communist Party USA.
It’s short for Armand Hammer, which was originally chosen as a pun on the Communist Arm and Hammer logo of the USSR.
The symbol of the USSR was a hammer and sickle. The symbol of the Socialist Labor Party of America, founded in 1877, was an arm holding a hammer. Julius Hammer was a member of this party before he helped start the Communist Party USA.
Yeah, I wrote that too fast. Thanks.