Kenny, they're looking pretty darn good. With respect to your airbrush idea, yes, that might work if you go lightly. What I and a lot of modelers do is "dry brush" the brick color on the ad (dry brushing, if you're not familiar with the technique, is putting a little paint on the end of a soft, flat brush, wiping almost all off on a paper towel until almost nothing comes off, then lightly brushing with vertical strokes. You can see the remnants of the paint go on very very slowly and easily control it based on how much pressure you put on the brush. This will make the ad fade more into the brick and seem more like it's painted on. You can also try some white/off white with the same technique and that will give it a old faded look).
Jerrman
