Not slots, but you hear an awful lot of shouting at the horses in Sigma Derby, and also at athletes in the sports book. I'm not saying it's necessarily superstition, but the effect is zero.
People fingering the coin return slot getting it ready.
I did this in college quite often.
I've seen latinos put pictures of their children on the machine along with a crucifix.
There is one guy I see quite often who pays the standard three reel slots and covers the entire area with a magazine.
Less superstition and more practical! See, this guy knows that he can't do a thing to tilt it in his favor, so might as well just keep mashing that big button and catch up on your reading until you get the elusive hand pay lockup!
Their thinking was that if the belly glass was hot, it meant the game was played more and thusly had a better chance of paying out.
It must have completely escaped them that there is a flourescent bulb right behind the belly glass which heats up the longer the light is on........
It pains me to say that my family members were amonst the ones most firmly believing in this superstition :)
I rarely pursued the high speed play of AP, and slow down on bigger hands.
The biggest fad I've seen in influencing (unsuccessfully) slot machines from other people is to rub the area on the screen where you needed a wild or bonus. Sometimes they tap the machine, to force the jackpot out? While it seems kinda absurd this is actually the most extreme I've seen people do to a slot, what are some really crazy superstitious things you've seen people do? Anyone jump out from the chair and do a 360 around it to "confuse the machine"? Or pull cards and cash out, and then stick them both back in?
I watched a woman cash out and then put the ticket back in over and over in an attempt to convince the machine was a new player each time since she believed it paid better initially to keep people playing (I asked). She also removed and inserted her club card over and over. I've watched many players run the screen or make the sign of the cross on it. One guy was tapping it (banging it is probably a more accurate description) that he caused it to error out with an open door code.