The name also comes from the John Sturges-directed movie starring Spencer Tracy, Bad Day at Black Rock (1955). An article titled "Bad Rap at Black Rock" is in the New York Times, 19 August 1975, pg. 31.
NBC studios are located at "30 Rock" (for "Rockefeller"). The old ABC offices were called "Hard Rock." There is a Hard Rock Cafe; "Hard Rock" is not in circulation at ABC.
13 March 1966, New York Times, pg. 20:
The American Broadcasting Company, whose radio station here specializes in rock 'n' roll music, recently moved into its new building on the Avenue of the Americas, right next door to the black granite building of the Columbia Broadcasting System. Two blocks south is 30 Rockefeller Plaza, home of NBC. Now that all three networks are lined up in a row, industryites refer to them as 30 Rock, Black Rock and Hard Rock.
1 April 1970, New York Times, pg. 44:
On the eastside the C.B.S. Building (dubbed Black Rock by office workers because of possible bad days inside its black stone colonnaded facings) is set off by tiny lights on trees in its sunken set-back plaza.