Why does the "hand" cursor in macOS have three vertical lines?
It's a housekeeping, or butler's glove - similar to the ones Mickey Mouse wears.
The 'indentation' actually is on the underside in real life, & is usually a button-fastener, but liberty has been taken to give a more skeuomorphic look.
A tradition since at least Victorian times. A symbol of cleanliness & discreet, professional service.
More images at Alamy - https://www.alamy.com/stock-photo/white-gloves-butler.html