I created a simple model in Tinkercad to let family members know when someone is using the bathroom. Can eliminate unwanted surprises.

The main base can be printed in different colors with pause and filament change at desired layer. 

Enter sign is to be printed separately and it will slide in the base. 

The cover will slide and select Enter od Do Not Enter parts accordingly. Stopper part prevents the cover from coming out, and can be fixed in place either with a drop of glue or a small piece of filament.

Pins will connect the handle to the cover.