What does "dry transfer" mean ?

They used to be called "rub-ons" as you apply them by placing them on the object and then rubbing them with a stylus or pencil until they separate from the backing. The ones today are much better and at least for armor modeling the ones from Archer Fine Transfers are incredible.
You can also rub them onto a sheet of clear decal backing and after coating them with a fixative (Micro makes a decal coating which works fine) you can then use them like any other wet-transfer (waterslide) decal.
Cookie Sewell

thx - any idea how much pressure is needed to transfer? I plan to use them on the standard Verlinden plaster diorama buildings. Will it leave an impression in the soft plaster? Not a desirable effect as these slogans were most likely brushed on walls.
Craig

A moderate pressure. The tool used is almost more important than the actual pressure. Some companies that sell them offer a teflon or nylon tool. I do NOT recommend a pencil or pen point. I used the back of a fine paint brush. One can round a piece of 1/8 inch dowel into a hemisphere and that will work, but painting and smoothing to a glossy finish works better. You do not want a sharp point- that will tear the backing (fronting?) paper. You need to make sure you rub over the entire transfer to get good adhesion- something that also says don't use something too sharp. The bigger the radius the more you get pressure everywhere.
Since the letters stand out slightly from the surface, some folks use this to make casting "logo" imprints. They are painted same color as the part, but the raise letters show slightly. Works well.