After extensive* searching on the web with multiple search engines, I was (very surprisingly) unable to find any information about this symbol - which is honestly absurd, considering just how often I've encountered this symbol myself while disassembling PCs and other electronic equipment.
I was also unable to find it on any disassembly guide or PCB symbol chart.
This leads me to believe that this is some sort of informal standard used by PCB/equipment designers. It may very possibly be a regional thing too, since all my searches were in English.
Here's an incomplete list of stuff I've seen the symbol on, in case it helps someone with more experience identify it:
- A 2001 Yamaha Synth
- A 2012 HP All-in-one
- A 2007 Sony home theater
- A 1998 HP Brio tower
- Various HDD enclosures
*Most of my searches were combinations of the following terms (tried both with and without double quotes), on Google and DuckDuckGo:
pcb, mounting, hole, screw, symbol, arrow, pointer, disassembly, pdf, schematic.