Why does the "hand" cursor in macOS have three vertical lines? What are the three vertical bars in the middle of the cursor supposed to represent?
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, &amp; 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 &amp; discreet, professional service.

More images at Alamy - https://www.alamy.com/stock-photo/white-gloves-butler.html