It was also quiet in the new canon. She got outted as Vader's daughter as a political hit job in the new one.
That's actually a smart move on part of their opponents.
The Sith being public knowledge wasn't really known about but a line in the movie references it.
Apparently be Palpatine broadcast the Sith thing in Minecraft.
After discovering this message (on this forum) I listened to the broadcast. Frankly, your average galactic citizen who can't really understand the reference.
He might recognize the Emperor's voice (even if we don't know if he was fond of public appearances, news anchor would certainly comment the broadcast and ask an expert who would identify him, reminding the younger audiences about that Emperor 25 years ago). I am not joking, if suddenly your TV broadcasted the voice of Jimmy Carter, would you identify him immediately (provided you're a US resident... chances are most citizen of the Galactic Empire were more concerned with local rulership and the broadcast would be as obscure as an American hearing the voice of Javier Perez de Cuellar. Not sure if it would sound immediately recognizable...
Anyway, so someone identified as the late Emperor by reliable sources says to the universe:
Late Sheev Palpatine former Emperor of the Galaxy former Senator of Naboo said:At last the work of generations is complete. The great error is corrected. The day of victory is at hand. The day of revenge. The day of the Sith.
Jedis would know about the Sith being back, but they'd know even without Palpatine mentioning it, since the Jedi knew that he's a Sith Lord. Most galactic citizen... they'd fear the revenge of their former Emperor, hope to get a good place in the new administration of the galaxy if they are members of the First Order, learn that some error has been corrected (maybe they fired their former safety engineer and started to build waist-high railings around the bottomless pits featured in their Supreme Leaders' thronerooms?) and that the day of revenge will come. Then, a strange phrase about the day of the scythe, certainly alluding that the revenge would be deadly. And that the Emperor has a strange way of pronouncing scythe. He must be saying tomahto as well. But I am not sure the sybillline broadcast would make the Sith "public knowledge". The Jedi removed knowledge of them for thousands of years and Palpatine stuck to the rule of two during his time as an Emperor... even some of the OT generals didn't think force power existed (despite having certainly lived and been a junior officer during the last day of the republic...)