He made it clear we cannot even hang the banner inside the windows to be seen from the outside.Has anyone had this happen to them and have they found a way around it?  

Yeah maybe stay away from acrylic, use a kit from Lowes like @Nicole Pettis said, you'll need two kits for a bath and shower - OPEN A WINDOW, its has a horrible smell that is intense. 

The room is in the basement and has no windows. 

The basement unit has no openable windows.

Here is a photo of my window.

If the job is small enough like electrical upgrade, copper pipe change-out, changing windows, etc..., going out the truck to get his numbers straight for a quick 10-15 minutes is typical. 

I have never used it on shower glass but it worked pretty decent on my fathers old car window.

You can just write the info on a regular For Rent sign or it lets you print a free one, which I assume you can put in the window or something.

I have not installed any wood windows.

A new window would also help and their reasonay priced.