Hints to Sauron's Identity That Are Noticeable Only on Rewatch
If you read anything related to The Lords of the Rings: The Rings of Power on the Internet, you know that Halbrand is actually Sauron.
Well, the majority of people discussing The Rings of Power were pointing that Halbrand = Sauron far before the confirmation in Episode 8. Some of the hints regarding Halbrand's real identity were about as subtle as a sledgehammer, starting from his first appearance.
Others, however, required viewers to pay more attention. Recently users on Reddit created a thread devoted to the hints they've noticed only when re-watching the show.
There are numerous examples, starting with the fact that Halbrand lost consciousness a couple of times during the show, but never ever appeared sleeping, even when he was in his bed at night (in line with Sauron's description as "sleepless malice" in Lord of the Rings and Galadriel's "Evil does not sleep" words in the show).
As during the course of the show Sauron's ambitions gradually reignite, you see bigger and bigger flames showing up in background behind "Halbrand"; particularly in scenes where he starts exhibiting skills and personality of Sauron.
There are moments, when Halbrand simply assumes a deadpan expression and stares into nothingness, without blinking. Then, like he has switch in his head, he turns on the Halbrand persona again and acts all friendly. There are camera shifts, with perspective switching to Halbrand when Sauron is mentioned by other characters or someone says something to the effect of "evil is among us".
Halbrand is very knowledgeable about things Sauron should know very well, from smithcraft to geography of the lands that later will become Mordor. He is, of course, a much better fighter than he lets on, and he survives injuries that should not be humanly possible to survive – not like this says much by itself in this show, but in combination with everything else… And in a number of scenes, such as on the raft, or in the prison, he is explicitly shown to be a manipulative person.
All in all, on repeat watching it is obvious that the show hardly ever misses an opportunity to hint that Halbrand is Sauron in any dialogue or scene involving him. The fact that some people actually did not believe this until the reveal is more surprising than the fact of Halbrand = Sauron being the prevalent fan theory before said reveal.