I recently found that someone used pawns to mark key squares. I didn't find it funny to start studying the position to later read "I marked these other squares with white pawns"...
But maybe the PGN reader can be improved to allow us to mark squares? maybe even draw arrows, something like this example, the example was created using
1.e4 d5<Ad7d5B><Ce4R> 2.d4 Nc6<Ad1h5B><Cf7R><Be4R>.
As you can see, their shortcut is something like (A for a-rrow, B for b-order, C for background c-olor) + (target square) + (first letter of common colors) wrapped in
<...> just after the move.
Is it possible to do something similar?