I added a color change for the border on the base and the letters on the insert. Fully assembled, the model is 4.75mm thick. When adding your word(s) to the insert in the slicer, make them 2mm in height, which will make them flush with the base border. Tolerances are pretty close. The model you see here press fits together. You can use glue or two sided tape if yours is loose.
The author remixed this model.
Inspired by @MadTNOTN, I wanted the three color print, but only having a single extruder MK4, I decided to make the base frame and insert separate parts. Using color changes in the slicer and adding my own text as a modifier to the insert, you can duplicate this sign as well as make your own custom sign.