Here is a funny example where Caligula's father Germancius was defaced and not him, probably in error.
Damnatio memoriae is the Latin phrase literally meaning "condemnation of memory" in the sense of a judgment that a person must not be remembered. It was a form of dishonor that could be passed by the Roman Senate upon traitors or others who brought discredit to the Roman State. The intent was to erase someone from history, a task somewhat easier in ancient times, when documentation was much sparser.
The sense of the expression damnatio memoriae and of the sanction is to cancel every trace of the person from the life of Rome, as if he had never existed, in order to preserve the honour of the city; in a city that stressed the social appearance, respectability and the pride of being a true Roman as a fundamental requirement of the citizen, it was perhaps the most severe punishment.
In Ancient Rome, the practice of damnatio memoriae was the condemnation of Roman elites and emperors after their deaths. If the Senate or a later emperor did not like the acts of an individual, they could have his property seized, his name erased and his statues reworked. Because there is an economic incentive to seize property and rework statues anyway, historians and archaeologists have had difficulty determining when official damnatio memoriae actually took place, although it seems to have been quite rare.
Historians sometimes use the phrase de facto damnatio memoriae when the condemnation is not official. Among those few who did suffer legal damnatio memoriae were Sejanus, who had conspired against emperor Tiberius in 31, and later Livilla, who was revealed to be his accomplice. Only three emperors are known to have officially received a damnatio memoriae. These were Domitian whose violent death in 96 ended the Flavian Dynasty, the co-emperor Publius Septimius Geta, whose memory was publicly expunged by his co-emperor brother Caracalla after he murdered him in 211, and in 311 Maximian, who was captured by Constantine the Great and then encouraged to commit suicide.
Any truly effective damnatio memoriae would not be noticeable to later historians, since, by definition, it would entail the complete and total erasure of the individual in question from the historical record. However, since all political figures have allies as well as enemies, it was difficult to implement the practice completely. For instance, the Senate wanted to condemn the memory of Caligula, but Claudius prevented this. Nero was declared an enemy of the state by the Senate but then given an enormous funeral honoring him after his death by Vitellius. While statues of some emperors were destroyed or reworked after their death, others were erected. Also, many coins with the images of the discredited person continued to circulate. A particularly large number exist with Geta's image.
No emperor suffered damnatio memoriae more than Gaius Caligula. Here are numerous examples from the Gary R. Wilson Collection:
The "C" for Gaius is hammered out on this Nero and Drusus dupondius issued by Caligula.
The "C" is filed away in this example.
Another with the "C" obliterated.
Here we see a scratch going from Caligula's ear, across his face and out into the field.
Here is another unpopular emperor, at least at the time of his death by suicide, Nero. Notice the gouge across his neck.