or thanking you... They are merely waving their sponsor's ad plastered on their bats for all cameras to record for posterity. Or so says this article in the DNA.

Excerpts:

Batsmen are instructed to lift their bats towards the pavilion each time they crack a fifty to ensure adequate TV exposure for the brand plastered on it as well as twirl around to allow enough time for photographers to capture the image. Bats are also not hung down when a player walks to the pavilion after a good knock as he has instructions to wave it to the crowd and the cameras milking additional publicity. The longer the time spent and more the runs scored all have performance based clauses which influence the way the batsman behaves out in the field.