I will let my last guess stand so we can start eliminating airports/heliports but I imagine it is wrong as I should know that OAK (even the present day GA area/north field; not sure when the newer airline terminal complex and massive fill in the bay to create runway 11/29 were completed) to downtown Oakland is more than 1.8 miles.
Originally Posted by
guv1976
According to the Wikipedia entry for the airline, the Downtown Oakland Heliport atop the AlcoPark garage was coded JOK.
Here's an article on the defunct heliport complete with photo of an SFO Helicopter helicopter:
https://localwiki.org/oakland/Heliport