S1R

5 miles off Santa Cruz, CA.

Probably a pirate operation!
It was almost impossible to obtain an amateur radio license aboard ships at this time. Some would make up a callsign and operate undercover.
Other known Pirate callsigns used from ships were BRJ, R5U, B4UP, VZX4X.

QSL Patrick Rigg Collection
Info courtesy of N2BTD