My current girlfriend goes into what I call "grap" mode before she's about to have an orgasm. She'll start grabbing my back, arms, anything that she can get her hands on. I can also feel her spasms around my cock. Many times they've been so powerful that she forces my cock out of her vagina.
One woman I used to have regular sex with was quite the squirter. When I was going down on her, I could feel her squirting into my mouth. If I was inside of her, I could feel her juices start to run down my cock and legs. Sex with her was messy, but whenever she visited, she always brought along "wet" pads.
With most other women, I've noticed vaginal spasms, increased breathing rate, "grasping", and flushing of the face and lips prior to and during orgasm. Some have probably faked it but have been kind enough to tell me they have cum. At least one hadn't ever had an orgasm, even from her own hand.