After the end of the war in Ethiopia in 1937, the Corps of "Polizia Coloniale" (Colonial Police) was created to take the role of the police in the colonies in Africa (Libya, Ethiopia and Somalia) and it started issueing its own license plates in Mach 1938. The first picture, though it's of very poor quality, shows a plate used on these vehicles: there was the bright blue print "Polizia Coloniale" in two lines followed by a black number.
Picture 1: 1936-1939
Later, when the provinces of Libya became part of the metropolitan district, the name of the Corps was changed and in 1939 it became "Polizia dell'Africa Italiana" (Police of Italian Africa), shortly known as P.A.I. It had got armoured cars, light tanks, motorcycles, motor-tricycles and cars: in total they were about 1.000 vehicles and as many motorcycles. When the Italian empire fell, the P.A.I. forces were moved in Rome with duties of public order until the liberation of the city in June 1944: then the corps was released and all its vehicles were taken by the police.
In the second picture you can see a P.A.I. plate, with the letters P.A.I. on the top line (at the beginning the letters P.A.I. were lght blue, but after only one month they became red) and a number of 4 black digits on the bottom. You can also find a full picture of the armoured vehicle this plate was taken from in the old photo gallery (picture 10).
The third picture shows a front motorcycle plate, mounted on the mudguard as it happened for the motorcycles of the Regio Esercito (PAI 001011).
Picture 2: 1939-1944
Picture 3: 1939-1944 (motorcycle)
There was also another plate with the full print "Polizia Africa Italiana" placed over the number and all the characters were red, as you can see in the fourth picture. I don't know the difference from the previous kind of plat that was much more common.
Picture 4: Polizia Africa Italiana
The first three picture are taken from the book "P.A.I. Polizia dell'Africa Italiana" by Raffaele Girlando and I received the fourth picture from Ernesto Vitetti who kindly sent to me. I must also thank Roberto Pola so very much because he first told me about P.A.I. plates, sent me the fist three pictures and gave me many details about them, and Paolo Mazzini who explained me the plates of the Colonial Police.