A few days ago I made some shots from the area around the place where I live.
Karlsruhe was heavily bombed during WWII, although not that bad like Köln or Dresden.
Until the present day, you can see the markings of the Air-Raid-Shelters (LSR or Luftschutzraum in german) which were painted next to or above the basements windows.
The arrows clearly mark the position of such an LSR in case the house on top collapses and rubble blocks the way out.
I don't know much about what the letters mean. They might classify the size of the LSR.
In Karlsruhe you can see pretty clearly where the shit had hit the fan. In a row of intact hundred years old brick and sand-stone buildings, you often find some ugly 50ies fast-built house.
I hope this might help some people who try to recreate dioramas or tabletop terrain of german cities of these days, like Olivier does. Visit his blog, if you do not already know it. It's amazing, what he's putting on the table :)