What does this button do?

Question

Windows

If you set a four-digit pin in Windows 8.1 as an authorization method, a numeric keypad appears when you enter it. But what does the bottom left button in the form of a square sun do? I click, nothing happens, I didn’t find an answer in Google (to be honest, I don’t even know how to formulate the request, I tried this and that, but everything is past).
Screenshot - https://onedrive.live.com/redir?resid=7D8B44ABEF05...

Answer 1

answers.microsoft.com/en-us/windows/forum/windowsr...
In a nutshell, turn on/off button blinking when entering a PIN code.