5 fingers in Greece means moutza or mountza, which is a traditional as well as severe insulting gesture in Greece.
Holding the 5 fingers up with an open palm facing outward is the moutza (or mountza), a traditional and severe insulting gesture in Greece.
Instead of meaning the number 5 or "stop" like it does in North America, the 5 fingers up with an open palm facing outward is used to express a persons deep contempt or insult, which is roughly equivalent to giving someone "the middle finger" such as in America.
The 5 fingers up with an open palm facing outward gesture in Greece dates back to the Byzantine Empire and criminals were also paraded through town on donkeys with their faces smeared with dirt, ash, or excrement (moutzos), using an open palm.
And pushing an open hand toward someone also implies wiping filth in their face or telling them "go to hell".
And the closer the hand is pushed toward the persons face, or if it's done with both hands striking together, (a double moutza), the more aggressive and the more insulting it is.
Tourists also often accidentally offend locals in Greece, when casually waving with an open palm or trying to signal the number 5.
Instead, as a tourist, you should keep your fingers facing sideways or close together, instead of shoving an open, rigid palm toward someone, when waving or signaling properly in Greece.