What Does it Mean to be Trespassed from a Store

What does it mean when people say that they've been trespassed from a store?

Can you be trespassed from a store if you don't sign anything? If so, how do you know that you've been trespassed.

It means that the store has told you that if you return to their premises, they will have you charged with the crime of trespassing.

You don't need to sign anything. You know you have been banned from the store when they tell you that you're banned.