NOTE: For specific countries, sometimes the Wikipedia page will be more exhaustive and vice versa, so always check both
Prohibitory traffic sign - Wikimedia Commons
Speed limit road signs - Wikimedia Commons
Warning road sign - Wikimedia Commons
Mandatory traffic sign - Wikimedia Commons
Yield sign - Wikimedia Commons
Turn road sign - Wikimedia Commons
Crossing signs - Wikimedia Commons
Comparison of European road signs - Wikipedia
Comparison of traffic signs in English-speaking territories - Wikipedia
Comparison of MUTCD-influenced traffic signs - Wikipedia
Traffic sign - Wikimedia Commons
User:Fry1989 - Wikimedia Commons