Regulators are nonverbal signals serving as informal rules that command the flow of conversation between or among people.  They are behaviors that monitor, control. coordinate, or maintain the speech of the speaker (DeVito, 2005). 

Examples:

Head nod: encourages the speaker to keep talking.
Lean forward and open mouth: tells the speaker that you want to interject.
Hand up: indicates for the speaker to stop.
Eye contact: informs the speaker you are engaged.