Is it a foul to touch shooting player's hand?

NO, there is no actual "written rule" in the book regarding this behaviour. However 99% of all refs. will either give a warning or call a tech. foul if the defender purposefully yells out anything during a shot attempt; it comes down to etiquette and sportsmanship. Many refs. consider this "trash talk" and will hand out a tech. for this reason; besides it's just looks bad doing it.