Around Rome, I noticed many numbered tiles (most with four digits, and all with a white background and blue text) around the city. An example is shown below on the right of the image.
Some of these tiles were placed at the entrances of historically important buildings (for example, Santi Quatro Coronati has a numbered tile), but many were at addresses with no discernable importance. I also verified that the number on the tile did not correspond to the street number. (This is evident, for example, for the property in the picture above; the street number is 28).
What is the significance of locations with these tiles? Is there a system behind their numbering / a list of all the locations of the tiles? More images are available in this album.