It's a common Western form of greeting someone. For more information check the link below:

https://en.wikipedia.org/wiki/Hat_tip


(Ps. Although people do tip their hats, another form in basic society is simply to pretend to tip with a small gesture or salute. Since it is too hard to make all hats or even a few compatible with a taunt, Krunkidile and other contributors simply made it as the gesture. It still stays true to the artform of tipping your hat. I hope this helps with any confusion.)