I thought of this question after reading another one.
Kyle Reese explains to Sarah Connor why he couldn't just shoot the terminator before it tried to kill her in the original movie.
REESE: Pay attention. The 600 series had rubber skin. We spotted them easy. But these are new. They look human. Sweat, bad breath, everything. Very hard to spot. I had to wait 'til he moved on you before I could zero him.
He was in the dance club watching her and looking around for the terminator. Reese should have recognized the terminator before it made a move.
Wouldn't he know what Arnie style terminators look like?
Skynet made hundreds of them. Reese even admitted in the original movie that the new ones looked human and had bad breath. He would either know that from personal experience, because somebody told him, or whatever. He might even have had a photo of one since the resistance would probably take pictures of it and send the pictures to other resistance cells with a note, "New terminator model from Skynet. Shoot on sight."