Hand gestures should be used carefully when abroad, in case of misunderstandings. The cheery ‘thumbs-up’ used by the English and Americans (and lately, the Japanese) means ‘up yours’ in the Middle East, and ‘sit on this’ in Sardinia. In France, pressing a thumb against the fingertips means something is absolutely parfait, or just right; while in Egypt the same gesture means ‘stop right there’.
A typical American sign for ‘okay’, made by touching the tip of the thumb to the tip of the forefinger, and used internationally by scuba divers, is an insult in Brazil. In some countries, making the V sign can be negative, in others, positive; in Italy, if you reverse the V sign to make it akin to the English ‘victory’ sign, it approximates to ‘to hell with you’. In some countries, flicking your thumb across the teeth tells the other person he’s a cheapskate. Just about everywhere, grabbing the crook of your elbow and raising your fist is rude; similarly, grabbing your crotch rarely intimates a positive sentiment. In the Arab world, the middle finger pointed downwards and moving up and down, with the palm horizontal, equates to a raised middle finger in England.
Probably best to keep your hands by your side and nod courteously.