[zen21]

Amusingly the same number as for the legal code used to involuntarily detain someone for psychiatric evaluation.

[valdiorn]

Made fairly famous by Van Halen, who used it as both an album name and the name for his signature guitar amplifier (still in production, and very, very popular to this day).

https://en.wikipedia.org/wiki/5150_(album)

https://www.evhgear.com/gear/amplifiers