#1
At the start of the game.
#2
Flashback... it turned into Ulti in the next scene.
#3
The end of the game.
I'll ask you questions.
Consider why Rinoa took sudden-interest in Squall? Squall's attitude against Rinoa was rather terrible through out the whole story, he didn't care much but Rinoa is still interested. Why? I don't think it's because of his good looking because that's very hard to believe.
She automatically cares about him (even when they met for the first time) for what exactly reason? Think about it.
Look at #1, that's the start. At the dancing party, for the first time. Squall stared at Rinoa first, when Rinoa looked at him back, then she suddendly used her finger sign and smilied, then the story starts, what was the meaning of that?
What's your interception on her finger sign?
Is it some sort of control? Did she control him? During the end of the game, Squall has had so many flashbacks of her finger sign, wonder why?
My theory to all the questions above is that she used her finger sign as a ultimate move in order to controll Squall effectively. So she can use him to be her knight, or a love-mutation to have the potential of becoming Ulti in the future. OR! She used her finger sign to remind Squall who she really is because she KNOWS that they have met before (way past, because of Time Compression). Squall somehow got a deja-vu feeling and met her again, and there you go.
In the game, before Rinoa and Squall met, her (or Ulti) white feather dropped his sword from the sky, then later, they met again, she used her finger sign and so on. Makes sense to me.