To greet with a gesture.

Source: Imam an-Nawawi in Al-Masa'il al-Manthurah "sid: 70

Question:

The health of someone by bending his head down, make a gesture with his hand or the like - this is halaal (permissible) or not?

Answer:

To bow our heads are Makruh (dismissed) and in the same way, it is the health of your hand without the express greeting unless the person would be dumb. Then it is recommended that he greets with his hand. But if you come to visit are far away so combine his greeting orally and by hand.