The intro to “Don't Tread on Me” on Metallica's The Black Album quotes the melody of “America” from West Side Story.
“America” was composed by Leonard Bernstein for the 1957 musical West Side Story. Metallica incorporated that recognizable melody into the introduction of “Don't Tread on Me,” creating a musical reference that contrasts with the song's heavy-metal setting.
The song's title and imagery connect with the Gadsden flag, whose “Don't Tread on Me” motto also relates to the snake pictured on The Black Album's cover. This creates a link between the album's packaging and one of its tracks.
The reference is easy to miss because the quoted melody appears in the introduction rather than as the main vocal hook. It is also sometimes attributed generally to Bernstein without naming the musical; the more specific answer is West Side Story.