Strange icon in all system password boxes on Mojave 10.14.6

Question

For a few days, I've been seeing this very strange icon every time a system password box shows up. I have no idea what it means? Does anyone know? I do not have capslock on.

Answer 1

This seems to be a "Numlock" icon. Rebooting the machine made it disappear. What made it appear in the first place remains a mystery...