Fascio (1928-1944)

Fascism became a dictatorship in Italy in 1922 and the symbol of "fascio" was placed on the Italian rear plates from 1928, with the Royal Decre with the force of law n.3179 of December the 2^nd. It was a little convex circle of aluminum, almost always not painted, that was tightened through a hole and showed a "fascio littorio".
After the end of Fascism, this seal was not removed from the old license plates, though many people did it by themselves.
Click here to see some entire plates with the seal of fascio.

C.O.N.I. (1934-1948)

In 1934 front plates, previously arranged by the owner of the vehicle, started being manufactured by the "CONI" (Comitato Olimpico Nazionale Italiano... it means Italian National Olympic Committee) that kept the income of their sale: for this reason they had a small symbol with the print CONI inside. At the beginning it was rhomboid and was attached to the plate with a hole (picture 1), then later, from 1945 up to 1948, it became oval-shaped and was printed directly on the plate (picture 2).
Click here to see some entire plates with the seal of CONI.

Association of Disabled Men of the War (1944-1948)

From 1944, when fascism ended and the fascio was removed from the Italian plates, until 1948 the symbol of the "Associazione Mutilati e Invalidi di Guerra" (Association of disabled men of the war) was printed on the rear plates, though this association had been making plates since 1927. As you can see it was a thorn crown with three bayonets and the funds raised with these plates were given to the association. A collector told me that actually this symbol was introduced a bit earlier, around 1941 because he has got a picture of the plate "Roma 77344" that was issued on February 1941 and it has got the symbol of the association.
Click here to see some entire plates with the seal of the Association of Disabled Men of the War.

Italian Republic (1948-Today)

With Ministerial Decree of December the 7^th 1948 a new seal was introduced on the Italian license plates: it's a star with 5 ends inside a branch of olive tree and a branch of oak with the letters "R.I." in the middle, where RI means "Repubblica Italiana" (Italian Republic). Since then this symbol, with little changes in its size and position, has been used on all the Italian plates, except the military ones and those of the Red Cross. In particular this seal was rather bigger until 1951.

Provveditoriato Generale dello Stato (1985-2003)

Since 1985, when Italian plates started being made of metal after about 20 years where plastic was used, they have had also a little print placed in various parts and you can read it only under some conditions of the light. Its aim is to prove that the plae is authentic and make it harder to produce fake plates. This print is made by the letters PGS that stand for "Provveditoriato Generale dello Stato" followed by one of the following four codes:

These codes identify the type of reflective film used to build the plate: at the beginning, the two factories that produce Italian plates used different films (A1 in Rome and B1 in Foggia), so it was supposed erroneously that it indicated the factory. Of all the codes, B1 is the most widely used. Many thanks to Marcello Taverna for this information.

Ministero dell'Economia e delle Finanze (2003-Today)

In 2003, starting approximately from the series CH 000 CJ, the letters PGS that could be seen on the plates under some conditions of the light were changed with MEF, that stands for "Ministero dell'Economia e delle Finanze" (Ministry for the Economy and Finances). These new letters are followed by a code that identifies the type of reflective film used to build the plate according to the same table used before.
A picture of this code is not available yet.