I don’t think I’ve ever seen a ♫ music note symbol as a hotkey on a keyboard. Is this something some company has?
ThinkPads use a ☆ star symbol to try to communicate that it’s a user-defined function key. Probably chosen since stars are used to mark something special or a favorite.
https://support.lenovo.com/us/en/solutions/ht503647
I’d suggest a similar star. But a ★ solid star, just to avoid the possibility of Lenovo trying to claim that the ☆ star somehow belongs to them.