Plates issued between 1905 and 1927 had a red number as origin code (see table) followed by a serial number in black (digits had to be at least 3 cm in height) and all the plates issued before were substituted with these new plates. The numbers were issued by prefectures, but the plates were hand-made by the owner of the vehicle and this caused many different kinds of plates, as you can see in the pictures. Plates had a lead seal that linked them to the vehicle, as you can see in the second and in the fourth picture. All the plates issued before 1905 were replaced with these new plates and the same happened again when the plates with the new numbering format were introduced in 1927.
The first picture is a porcelain plate: it's supposed to have been issued in 1911 or 1912 due to its number and 63 means it comes from Torino. The second plate was also issued before 1927, very likely in 1909, and it is from Rome (number 55). Anyway it is not a porcelain, but it's made of painted metal and this shows that both kinds of plates existed; on the bottom right corner, even if it is not clear in the picture, you can read "N. Ceccarani - Via Milano 21 Roma" and that is the factory of the plate; while on the seal, again even if it is not clear in the picture, you can read "R.Prefettura N°55": as said at that time registration of vehicles was made at the prefecture.
Front plates were exactly like back plates: anyway sometimes they were directly painted on the radiator of the car to let it work better, as you can see in the third picture (Bébé of 1902 by Peugeot Croizat). I also saw some antique pictures with front plates with reversed colours, white digits on black background, but the reason of these strange plates is not clear yet and anyway they were not official (see the old photo gallery, picture 1).
The "Touring Club Italiano" made plates for its members: they had got the "TCI" symbol as you can see in the fourth picture (issued before 1910). The T.C.I. was founded in 1894 by people who loved travelling and were very interested in cars for this reason; it does still exist, produces maps and travelling books, gives assistance to drivers and helps solving all the problems related to the roads.
Mark Bacarelli collected a lot of interesting data about the plate of Arezzo of this time: if you want to see them, click here.
In this web site you can also find the highest numbers issued in each province with this numbering system: if you want to see them, click here.
Many thanks to Alessandro Libanore for the first two pictures and to Marcello Taverna for the fourth. The third picture is taken from the issue of December 1999 of "La Manovella".