Foul tip signal

[Paul L]

Although next to useless, the foul-tip signal does indicate when less than two strikes that you know the ball struck the bat, but that it was a foul tip, and thus not an out. Sort of like the little safe signal on a trapped catch.

OBR 6.05: "A batter is out when—
(a) His fair or foul fly ball (other than a foul tip) is legally caught by a fielder;"

I too give it mainly because my association trained me that way.