I can’t say that it will work any better for your printing situation than acetate, but why not try it using clear styrene? Acetate yellows with age and becomes brittle, too - I didn’t realise anyone was still using it for such purposes.
I called it acetate as a generic term, but upon looking at the package, it is called “Computer Grafix Printable plastic sheets”, for ink jet. I would think these are made so that the ink does not smear or smudge, but it does.
I like all of your suggestions. Thanks for the help.
A possible solution might be to print your signs on white paper and then photocopy them onto clear “overhead projector” slides. These are pretty durable and can be obtained in either black and white or color. They would not require any sealing.
Instead of printing directly on the window material, use decal paper, and apply the decals to the windows. I do this a lot, and it works very well.
Flip the image horizontally, so it becomes a mirror-image of what you want. Print that on the acetate, and then install it from the inside. When you turn the building around, the printing will be correct, and the image will be protected from smudging because it’s inside the glass, not on the surface.
don’t know what printer you have but if its a hp or epson it should work make sure you have the correct clear and you have to print on the correct side only the back side will smear