Touching the keypad number sign (#), also known as the pound key or the hash symbol, to confirm inputting credit card numbers or Social Security numbers or pin numbers or really the termination of any phone transaction, is a ubiquitous experience in the world of digital transaction. But we may not know that # was an abbreviation of lb, "pound by weight" in Latin, or this symbol's name is also octothorpe. In purely analog times, the pound key was not the number sign but a word re-invented to describe and 8-pointed image. In the 1960s, engineers at Bell Labs added the number sign to the telephone key pad as a way to send instructions to the central telephone operating system.
If you want to go down the octothorpe hole, check out Chris Messina's Medium article, "The Real Source of The Word 'Octothorpe'" from 2019.
