This may seem like a strange place to post this but I stumbled upon another model railroad forum (here) based in Germany that is devoted to American model railroading. I was doing a Google search looking for images of old signs and came across it. If you took high school German and remember anything (I did and I don't, or at least not much) you can see the great interest there is in Germany in modeling our railroads. I always thought of this hobby as being pretty provincial but I guess not. For some strange reason I have found this forum fascinating to look through. Looking at the dates posted it's not super-active, but apparently there is a contingent of Germans who are really unto us.
So anyway, supposedly on this site there is a link to pages upon pages of old sign imagery that can be downloaded and printed out. I haven't found it yet (my German is very rusty) but if anyone knows of a source, let me know. I seem to be zeroing in on the early 1960's as the era in which my layout will be set and signs from that time period would be helpful.