Xander: What's with the hand wave? You see that? Does that, like, mean something?
Willow: It's code. I think it breaks down to 'choo-choo!'
Anya: It probably means to follow him. That, or wait here for him.
Willow: [whispering.] Ask him.
Xander: [yelling.] Hey, Riley? What's the [hand gesture.] all about?
Riley: It means yell real loud so the vampires who don't know we're coming will have a sporting chance.
Xander: See, now he's all mad and sarcastic.
Willow: It's because you were doing all that yelling, Mr. Stealthy-pants.
Spike: Death is on your heels, baby. And sooner or later, it's gonna catch you. And part of you wants it. Not only to stop the fear and uncertainty, but because you're just a little bit in love with it.
Chosen answer: From what we see in the series, certain girls are identifiable as potential Slayers - Kendra clearly fell into this category. The identification method is presumably mystical in nature, but the Watchers' Council are pretty effective at that sort of thing, so they're quite good at tracking down the potentials ahead of time. Not perfect, though - it does appear that Buffy herself may have slipped through the net - certainly she had no inkling of what she was until she'd already taken on the role of Slayer. It is possible, however, that this was actually cultural - an American family would hardly be likely to turn over their daughter to some strange man for 'training', so the Watchers might have chosen to keep an eye on her covertly, whereas some other cultures (like Kendra's Jamaican parents) might be more willing to believe.
Tailkinker ★