"Rock Around the Clock" was a song by Bill Haley.
Behind the scenes
The third draft of the script called for Marty McFly to sing this song at the Enchantment Under the Sea dance, rather than "Johnny B. Goode" which made the final film. The song is, of course, another reference to clocks.
Although the song would have been unfamiliar in 1952, Marty's destination in earlier drafts, Rock Around the Clock was already somewhat of an "oldie" everywhere by November 12, 1955. This song, by Bill Haley and the Comets, had been released late in 1954, and had been featured in the film Blackboard Jungle in the spring of 1955. When the script called for Marty to travel to 1955, the choice of song was changed.