Some Assembly Required - S2-E2
Visible crew/equipment: As Buffy goes through the door with the "Keep Out" sign on it, the shadow of a camera can be seen on the left side of the door in the last few frames of the shot.
Visible crew/equipment: When Ampata agrees to go to the dance with Xander and they walk off down the hall, a shoe can be seen in the bottom right of the screen within the last few frames stepping into shot.
Visible crew/equipment: Right after Kane and Buffy's fight in the woods, in the shot right after Kane leaves, you can see set-lights above the clearing where they fought. (00:39:10)
I Only Have Eyes For You - S2-E19
Visible crew/equipment: When Xander opens his locker and the gross hand grabs him, if you use slow-mo when the shot is inside the locker looking out, you can see the white t-shirt of the man whose arm it is. (00:10:20)
I Only Have Eyes For You - S2-E19
Visible crew/equipment: After the history teacher writes, "Don't walk away from me, bitch!" on the chalk board, Buffy says to Xander, "I'm telling you, something weird is going on." As she says "something", a boom mic is reflected in the window behind her on the right.
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 ★