Signs can take absolutely no input in them. Even using the on-screen keyboard, it completely does not work. There is no way I have found to type in signs, and my keyboard works fine.
As far as I know, this glitch only exists on Windows 10 machines. Just place a sign and try to type. It won't.
Linked issues
Comments 3
This is a known issue. In the short term, pressing TAB on your keyboard or tapping the screen (since your device seems to have a touch screen) should allow you to type again. You need to do this every time you want to type after having left clicked the mouse.
This is a known issue. In the short term, pressing TAB on your keyboard or tapping the screen (since your device seems to have a touch screen) should allow you to type again. You need to do this every time you want to type after having left clicked the mouse.