The snake on Metallica's 1991 album cover was based on which flag?

The snake on Metallica's 1991 album cover was based on the Gadsden flag.

The cover places Metallica's angled logo in the upper-left corner and a coiled snake in the lower-right. The snake is derived from the Gadsden flag, an American historical flag associated with the motto “Don't Tread on Me.” That motto also became the title of one of the album's songs.

The original packaging used an extremely dark design. The logo and snake were embossed so subtly that they could almost disappear against the black background, which helped create the fan nickname “The Black Album.” Later editions made the emblems easier to see by rendering them in dark gray.

The cover has also prompted comparisons with fictional and real rock-album artwork. The band jokingly acknowledged similarities to Spinal Tap's fictional Smell the Glove, while Lars Ulrich noted that Status Quo's Hello! was another black-cover reference.