The OpenMower mainboard (mine is v0.11.x from the Gadgets By Vermut kit) has a neo pixel LED to show the various states. However, when the housing is closed, you cannot see it from the outside.
I had transparent polycarbonate 3d printer filament at home and tried to use it as a light guide to make the display visible from the outside. It works surprisingly well.
The system consists of the following simple components:
I used very little glue to prevent the filament from becoming opaque. I'm not afraid of the housing leaking and I think the glue will hold tight - but time will show ;)
Related links:
The author marked this model as their own original creation.