Thanks for the advice, Tae Shala. I have the Civ Gold edition (which includes PTW, but not Conquests). I've tried starting games from scratch (ie, normal, plain vanilla games, not scenarios or anything), but the labeled resource icons don't show up--which is odd, considering the fact that the original, non-labeled icons shouldn't exist anymore (at least not in their original directories).
As per the instructions in Skanky's download readme, I replaced the two files in the Art directory (resources.pcx) and the Art|city screen directory (CityIcons.pcx). The resources.pcx file is obviously the one that counts, and when I click on the file it pops up with the labels. The only logical explanation is that the game is drawing the resource icons from another location. At least, that's the only logical explanation to me. Perhaps someone else has some insight?