I stumbled across this over on the Consimworld website, where they were talking about making up maps for board wargames.
Its an archive of icons developed by Gerd Arntz for maps made up in the 1930s to 60s. Some of these look really useful! I"m not sure if anyone has posted this link here yet. If they have, then my apologies for the duplication.
Gerd Arntz Web Archive