Inflield Fly how to "declare" one

[lc_huxter]

What I am asking is pointing a finger in the air good enough. Or do you have to say "infield fly batter is out"

I say a finger is not good enough. How is a base runner suppose to know that you call one and they are safe and do not have to run. I know what the rule book says. With easy effort. Well any infield pop up is easy effort if you can catch.