The cash register sound comes from the mechanical tills once used in shops, where ringing a bell and opening the drawer signalled a completed sale. It was soon borrowed by cartoons, radio and television as a quick audio shorthand for money, and that association has stuck. Online, creators now use the same ka-ching in short videos, memes and streams whenever a deal, purchase or payday is shown, because listeners recognise it instantly even without seeing a till. Its simplicity is why it remains a staple of comedy and money-themed edits.