Heh, Yeah, you could also put "this week, discount urinal cakes" or some such thing.
Seriously though, hiding a window behind a louvered vent, like one you may see on an insulation blowing truck for example, would work well up top in the cabover section and you could obscure the glass with a thin white sheet of plastic. Pop that off, and you have a louvered window with natural light, pop off the louver, and you have a full window.
I have also seen those louvered vents on odd places too, it's all based on where they install the machinery in the truck, so one just above your desk would not look strange.