The group that I call with practice the following.
Plate Umpire makes the call..
during an infield fly rule we will touch the brim of our hat and show how many outs and then point up. This lets us know that we both are looking for this (IFR). If the batter hits into a possible infield fly, where if behind the plate I cannot quickly determine I will point up into the air, my partner will also do the same, at that time I will call: infield fly, fair, batters out.
NOTE if my partner has a better look at the call and does not point, I will usually not call the infield fly rule.
here is general rule....
Possible Infield Fly Situation
Some crews signal each other by first relaying the number of outs from the brim of their hats then signaling the infield fly. Another infield fly signal is done simply with the thumb pointing and moving upwards. A standard signal is to tap your left shoulder with your right palm indicating that the infield fly could be called. What is important is that play does not resume until all umpires are aware of the pending situation.
If the umpire determines that a player can make the catch with ordinary effort, then he/she can apply the rule.
IFR is called on each
Second baseman makes an effortless catch on the grass.
Second baseman is called off the catch and an outfielder makes the catch...if the catch could have been made by the second baseman with little effort..