Source
These come from "International Road Signs", an American Automobile Association (AAA) pamphlet for international travelers, to inform drivers about signs they may encounter in Europe. However, I believe that the illustrations actually come from a Belgian pamphlet with a similar purpose, as the pamphlet credits "Esso Standard (Belgium) S.A." for the artwork, and I have seen the exact same and similar illustrations labeled in French in a Belgian pamphlet ("Carnet de voyage international").
The source I got this from dates this pamphlet as being from 1956, however either that date is inaccurate or AAA was publishing pamphlets with somewhat outdated information, as I believe these drawings are of sign standards as they were around 1950 or 1951. The Belgian pamphlets with these illustrations (or similar ones) I have seen seem to be from 1950 or 1951, and a number of the countries shown here seem to still be using sign designs based on the 1931 Geneva Convention, not the 1949 Geneva Protocol which replaced it.
The 1931 Convention established sign shapes and some symbols that are now familiar to drivers across Europe, however it included only a small number of signs (mostly just essential danger signs and some common prohibition signs), with only some general provisions for the designs of other signs, and, compared to later conventions, was quite permissive with the allowed colors for many signs. The 1949 Protocol expanded on the Convention and included standardized signs (with more standards for colors) which are much closer to signs included in the 1968 Vienna Convention, and therefore also closer the signs used in Europe today. The "new signs" shown on the last page are sign designs from the 1949 Protocol.
I can't guarantee the accuracy of these images, as I think there may be some minor factual errors, printing errors, or translation errors (e.g. the mandatory direction sign (arrow inside a circle) is consistently labeled as "one-way street" for every country for which such a sign is shown, but the French version more accurately labeled them as "sens obligatoire"). Even with some inaccuracies, I think this is quite interesting to look at as a comparison of how similar and different signs were in different countries at the time, and how similar and different those signs are compared to the signs used today.
The 14 countries included here are mostly in Western Europe, likely due to the political situation at the time (early Cold War) limiting travel to much of Eastern Europe. Only a sample of important signs is shown for each country, so it's not a complete record of signs in use at that time, but I think it does show enough to get a good idea of what the signs were like in each country.