I was thinking about Terminator 2 recently. In the movie the T-1000 (Robert Patrick) doesn't explicitly do anything to reveal that he's a terminator until the scene in the mall hallway.
From a hypothetical perspective of someone who has seen only the first movie, one could have assumed that Robert Patrick's character was another resistance member sent to protect John Connor, with Arnold Schwarzenegger reprising his role of another terminator.
Looking up the original theatrical trailer they forego the idea and totally just tell you "Oh hey he's a terminator sent to protect John Connor."
I think it would be a pretty cool twist for someone to experience, watching the first Terminator then seeing T2. Although with all the Terminator movies since and the cultural knowledge of the franchise I would think it'd be pretty hard to find someone who didn't know.