GSK 783

From Memory Alpha, the free Star Trek reference

GSK 783 were the call letters of the private transmitter owned by George Samuel Kirk when he lived on Deneva in 2266.

His brother, James T. Kirk, ordered Uhura to signal this transmitter when she failed to receive a response from an official transmitter.

George's wife, Aurelan, responded on this transmitter. (TOS: "Operation -- Annihilate!")