Smiling for Thailand, means hello. And communicating with gestures Which is expressed with sincerity and joy by perhaps not to speak. He nodded to each other If you do not smile Sometimes it is bad manners at all.
A smile for the people, referring to greet and communication with posture. Which will be expressed sincere and happy by maybe don't talk, smile nod to each other, but if not smile. Sometimes it's bad manners. .