[Newbomb Turk]

It was once common to cut off the middle finger of your enemys captured archers making it hard to draw their bow.

Flipping the bird was one way to show you were still a danger to your enemy.

[Harmless Teddy Bear]

In quite a few countries a "thumbs up" sign is considered just as vulgar and for the same reason.

They would often cut off the thumb of captured swordsmen. No thumb means you can't handle a sword anymore.