In biker culture, the number 81 is often associated with the Hell's Angels Motorcycle Club. The number 8 represents the eighth letter of the alphabet, which is "H," and the number 1 represents the first letter, "A." Together, 81 stands for "HA," which is an abbreviation for Hell's Angels.
It's important to note that the meaning of numbers can vary within different motorcycle clubs or subcultures. In some cases, certain numbers or combinations may have specific meanings unique to a particular group or region.