For which engine? Deferred decals are ideal for laying out the loads of unique markings along a runway, but might not be suitable for this project (if it uses Forward rendering)
Thanks for the feedback guys. I made some adjustments to the decals, the wear was a little light and bright - should be better now. Updated original pics.
Loving the atmosphere, the one thing I would suggest are decals - put the icing on the cake, so to speak, by getting a little grime in the walls and floors.
So this is not a polygon plane placed in front of the wall? It's a layered shader? layered texture? or what? Here's one common way: http://wiki.polycount.com/Decal