You asked me in another thread if I would give an answer to this, so here goes:

There was nothing subtle about anything that happened between 49 BC and 27BC (when Caesar crossed the Rubicon and when Octavian took the name Augustus and devolved his powers to the state). It was about as subtle as World War One. By the end of the civil war with Antony, Octavian led an army of 300,000 according to the Res Gestae. They were levied from all over Italy and the provinces and fought another army of the same. This all happened after two other giant, continent-spanning civil wars. In between the wars you had the disastrous Second Triumvirate where Octavian and Antony led a pogrom against just about every other person with any political sway.

Rome's political system was based on a series of rules upheld by jealous aristocrats to make sure that other aristocrats didn't get too much power. It was a mutual agreement between the elite, and most of the elite died in those civil wars. The system was untenable. Even though he tried to restore it by filling the Senate with new blood as a censor or by changing consuls every month for a few years, it was clear that none of them would be able to balance his power. If you read the Res Gestae Augustus talks about the acts he did for the good of the city as a private citizen. He funded games, updated infrastructure, paid for the state subsidized grain, and much more. These were acts a magistrate or at least an elected commission would do, but now a private citizen was taking them over.

Augustus never outright declared himself a monarch. The republic ran much as it did before the first civil war but Augustus was running another government alongside it that held the real power. He also made sure to have a public presence by attending public events and putting images of himself all around (on the Altar of peace for example). People would know him, recognize him, and talk about him. They would know who he was and what he did. Rome ran on gossip and I suspect that political gossip would be the center (think Washington Post style section more than The Economist). Thus I think most Romans understood that Augustus was in charge and that the republic was long gone. After years of civil wars fought between jealous elites trying to prevent their rivals from getting to much power, most Romans probably thought this veiled monarchy was for the best.