My simple door sign has a total of 4 parts:

• frame
• plate with the text "Free"
• plate with the text "Occupied" and
• sliding (covering) door.

All parts cen  be printed separately, without support. Glue (CyanoAcrylate) the two plates with text into the frame. Finaly, the door will snap into the rails after applying minimal force. 

Hint: plate with text can easily “colored” (even on standard printer without MMU) by simple trick: in PrusaSlicer use color change for last “flat” layer and continue with changed (green or red) color up to the full height of the letters. Voilá!

I recommend to use WHITE PET-G for all parts, except letters. It looks great!

Print in 0,2mm resolution.

You can download attached Fusion360 model and make modifications to the text at will.