I have several sheets of 1/35 street signs, danger warnings, propaganda,
etc. from Dio-Art and Custom Dioramics.
Am not sure if these types of signs would have been painted directly
onto the brick or stucco walls or mounted onto wood/metal bases or
posted on bills like you see around walls of construction sites.
So, given that, ideas how to make the paper set onto the brick details
like a decal would set.
Saw a demo on this at a model railroad club meeting. Sand the back side
of the paper item to thin it as thin as possible, then apply it to the
surface wetted with water. Set it with an overcoat of thinned Elmers
glue - just a light coat. You can use an artist's brush to help settle
it into the low spots while wet, if required.
Once it's dry, weather as you like.
A similar technique is to coat the front of the paper with a layer of white
glue and let it dry. Soak in water for a few minutes, then gently scrub
the paper off the back. (Naturally you need a waterproof glue. Craft
stores even sell a product especially for transfering magazine & newspaper
photos onto craft projects; I think one brand name is "Decal-It".) You
might have to use sandpaper, but fingers are usually sufficient. The thin
film of glue will hold onto the top layer of paper fibers & ink, so you're
left with a thin flexible image. The more paper you scrub off, the more
transparent it will be, so you may need to apply it to a light surface or
paint the back before applying.
Another option is to buy some blank decal film and have the signs
color-copied onto the decal film. Clear decal film will give you
transparent decals. White decal film will give you opaque decals, but
you'll have to trim them carefully to eliminate unwanted white borders.
I don't recall "decopauge" relaxing paper enough so it would appear the, in
this case, a street sign would show as being painted directly onto brick. I
always thought of it as more of a plastic coating in general.