I wonder is sign language speakers have a gestural equivalent?

Grab the other person’s hand?

Many years ago, when I smoked, that was an excellent method of holding the floor while thinking through one’s comment.  You would start off with “Well. . .” and take a drag off of your cigarette, let out the smoke slowly then begin speaking.  I think that was the only thing I missed when I stopped smoking. 

Then I had to come up with meaningless substitutes like, “You make an excellent point, but. . .”,  “Interesting observation, however,. . .”, “If we consider it from a bit different perspective. . .”

Occam

Perhaps it is that science minded individuals are more involved in their own thoughts than that of others. Using “So” is a way to get such a minded character’s attention when appropriate conversation is lacking. I use “So” frequently to wake the absent minded from their musings.
“So, are you in there or what?”