Paper to styrene

Is the surface smooth or brickwork or ? I have put signs on painted brick walls with Elmers white glue, However, my signs were printed on a laser printer. Ink jet ink may run if it gets wet. But, you could seal it with clear matte spray before applying glue.

Pretty much smooth, though some will have a shallow "stucco" texture.

Sand the back of the signs. That will help them conform to the surface.

Okay, got it.  I'd never have thought of that.

What's the best adhesive?

White glue--see my first edited reply.

Sounds easy enough.  I'll let you know how it turns out.

Thanks.

This can, with a little practice and timing, produce a desirable effect for those wanting old faded signage.

A relatively simple paste-it-on with Elmer's No-wrinkle Rubber cement. I have contact adhesive but it is a bit too aggressive, the ink jet stuff started to run and smear.
Farmall sign is a print from the internet on standard paper.  Red River Valley  and Farmers Co-op are  Walthers decals from another kit. Sur-Sweet Feed Store.   Model is a Lionel Grain Elevator (styrene kit). 

Okay,  tried both ways on two different projects.  The rubber cement I used was old and lumpy but worker just great after I smoothed the bumps out of it with my fingers.

The Elmer's was easier to use, but a bit messier.

Both turned out beautifully.  The sanding is tedious, but really made it lay down nicely.

Thanks for the help.

I'm glad that worked out for you. Thanks for the update. Most often, we never hear how our suggestions or advice works out.

If I can get my furschlugginger computer to talk to my racksinfrankish camera I'll post pictures.  

(I probably shouldn't be allowed around any post 1885 technology, and certainly nothing with an electric current, anything magnetic, or items subject to the laws of gravity.)