A supervisor once told me that when I point out that strike I should keep my eyes forward. He said if I do it with no runners on base it will become a habit that will continue when there ARE runners on base, and that's the time looking away COULD be a problem (batter's interference, for example). He suggested pointing not toward the dugout but up the first baseline. I know of an NCAA CWS umpire who does it that way - I opted to just keep my eyes forward while still pointing out to the side.
I will agree with posters who said to "marry" the verbal and signal for the strike call. And yes, that is a hard habit to get into. And no, I still don't do it that way. Something about "old dog, new trick..."
JJ