I couldn’t have possibly found this site too soon: http://www.gatewaynmra.org/download.htm.
Besides photographs of six vintage building signs, there are also numerous other photographs for download that might be useful, and also some articles with really good tips.
Emphasis is more on serious modeling in HO or N scale than in toy-train O or S gauge, but in the case of the photographs, all that means is you have to print them bigger in order to use them. And the tips for assembling and improving models from kits hold regardless of type.
I also found this tutorial on lighting your railroad buildings with Christmas lights. Seeing as most places have them on sale for 50, 60, or 75 percent off while they last this time of year, the timing’s pretty good.
One guy in rec.models.railroad suggested using yellow LEDs to light your buildings, but seeing as a strand of Christmas lights is dirt cheap and I don’t have anything to cannibalize yellow LEDs from, I may go the Christmas light route first.