Among other political groups, the Italian Communists seem to inspire a great deal of graffiti. Italy has had a communist party in one form or another since 1921, but the party has split and merged with factions within itself and with other parts of the Italian left on a number of occasions. All of this makes its history difficult to follow. Amusingly, the top of the Wikipedia site on the topic attempts to summarize the history of organized communism in Italy and fails to do so in a single paragraph. Today, communists are a political minority. Italy has a parliamentary system and the current Italian government is run by a rightist coalition headed by the Prime Minister, Silvio Berlusconi. None of the coalitions containing communist parties hold any seats in the parliament. The marginal nature of Italy's far left may help create the need for graffiti as political speech.
Walking home from the Sede, I found a great deal of communist graffiti on the walls lining the Tiber; both on the Largo Avention and Largo Pierleoni. The image above is an example of this. It declares "Rome Free and Red" with a star following. The graffiti is actually more easily viewed when riding by on a bus than it is when walking by. It appears that the artist of this particular piece is attempting to advertise his or her political views to passing motorized traffic more than to those walking by.
Not all of of the communist graffiti in Rome is aimed at passing traffic. Some of it is smaller and aimed at the sidewalk instead of the street. Yesterday, I found this hammer and sickle freshly painted on an electrical box on the Via del Circo Massimo. Given the covering of the trees in the parkway and direction of the graffiti, it is most likely intended for those passing on foot. The appeals that these pieces make are not particularly complicated; appearing to do more to simply reiterate the existence of the marginalized political left in Italy than anything else. Some other pieces seem to have more of a targeted meaning.
For example, I found this piece spray-painted on an automated currency exchange across the street from the steps that lead up to the Capitoline Museums. This piece is clearly meant for an audience of foreigners. First, this can be presumed because it is written in English and not in Italian as most of the other pieces of communist graffiti that I have found. Second, it is written across a currency exchange and foreigners presumably use these machines more than anyone else. Additionally, the machine, being across the street from the Capitoline Museums, and located near the capitol hill and downtown is placed in a prime tourist location. In addition to the message being conveyed, this particular piece of graffiti splashes paint across the screen that is used to complete the transaction. This makes it impossible for anyone using the machine to ignore its presence. It may also make the machine unusable, but I have not tested this hypothesis.