How do hand signals vary between countries?
Both question linked by Neil are rather comprehensive for the US and UK. Wikipedia (though not the greatest resource) seems to have a nice, even if short, list of arm signals in various countries.

I live in Denmark, and while I couldn't find a trusted resource for it (there are a number of blog posts, though), I'd say the convention is to use straight left and right arm signals. And in reality they are something between a straight and a bent arm, so it only matters which arm is used.

Finally, Lithuanian traffic rules (note: it's in Lithuanian) indicate the following:


To turn right, use straight right arm or bent left arm
To turn left, use straight left arm or bent right arm
To stop, use either left or right arm straight up