I don't know about decals, but a number of years ago Chartpak used to make dry transfers of people in various sizes for use on architectural drawings. They also had a number of lettering sheets in various fonts which could be used to make signs on a model layout.
Why not print them on paper, put them a fraction of an inch inside of window? Will obscure them just enough to you from seeing them too clearly, plus provide a slight amount of perspective- so it doesn't look plastered onto the window.