Which is an example of Roman propaganda?

You are actually correct to categorize your question under "newspapers and magazines"-- there were no magazines yet, but perhaps the first newspaper was published by the Roman emperor in 59 BCE, and it absolutely was an example of Propaganda: the "Acta Diurna," the Daily Acts, or Daily Public Notices. The government posted them in places where they would get a wide audience. But the Acta never told the entire story: they did not contain any criticism of government policies nor present anything other than positive news about the emperor and the government and the people the government considered important. Thus, the Acta only let the people know what the emperor wanted them to know. There was no freedom of the press yet-- the government published the Acta, and controlled the information that was released to the Roman public.