When this effect happens on a plastic model using decal paper it simply means that it has not bonded to the model effectively. You then need to add more setting solution to try and get it to snuggle down into and around rivets etc. I would suggest that you are adding your decal to a porous surface. The idea is to paint an area the size of your sign with a clear gloss coat before laying down the decal, decals will not adhere to flat (dull) porous surfaces.
Try lifting your sign paint the area with a clear gloss coat, let it dry then add your decal with the decal setting solution. The same applies if you are using the decal on a plastic surface.
If you then see any dullness (looks a bit silvery ) under the decal film add more setting solution carefully. You can use a very small pin to make a few small holes where the dullness is to add the solution just in that spot. Do not touch the decal as it will move and all will be lost while it is wet.
Once all clear add a coat of dull coat and it should look hunky dory.
Trust this helps.
This is an excellent thread...some really helpful tips (and those signs are great). As far as I can tell, no one has mentioned INK vis-a-vie the making of decals/signs. Most inkjet printer inks have a problem with color degredation. That is to say they fade over time. [If you have some older photos you printed on an inkjet printer, compare the color density to a recently printed image). The culprit here is a combination of air pollution (easily eliminated with a matt overspray...on both side of the picture) and (more likely) UV radiation (a serious problem if using fluorescent lighting).
There is a couple of ways around this problem: 1) use archival quality ink cartridges or take your laser decal film to a photocopy store (such as Staples) and have them print it on one of their high-end color laser copiers.
Just a suggestion...I enjoyed the thread.
____________________ "Keeping my hand on the throttle, and my eyes on the rail."
I used the same technique with wood as I do brick by sanding the back of the paper. If the base sign I'm using is wood, I'll use an xacto knife to make vertical or horizontal lines in the Basswood or Balsa.
Thanks for looking,
For a different type of sign, I wanted a street banner and discovered (probably everybody except me knew you could do it!) that I could get my old Epson R300 inkjet printer to print on fabric.
I attached ordinary bed sheeting material to a piece of very thin A4 card (heavy grade printer paper would probably work) with half a dozen strips of double sided Sellotape to keep the material from "billowing" and fed it through the printer on "photo" setting. No smudges or smearing and it dried pretty quickly. The banner was then cut to size and hung on the layout.