Now if you want to talk of the duties of a uniformed security patrol duly authorized to protect private property you will find all they can usually do is request any trespassers leave or request persons wait for the police.Only if the security person sees a crime being committed or is absolutely certain the suspect has committed a crime can the security person effect a citizen's arrest.
Again on public streets and sidewalks,parks,etc. the Neighborhood Watch would have no more authority than any other citizen to stop a "suspicious person" and question that person.And the stop ought to start off "Hello,I (or we) are members of the Neighborhood Watch here ,and I (or we) wondered if you need assistance." Establish clearly who you are,and begin a non-accusatory conversation.Acting the part of the "take-charge cop wannabee " and confronting people will only cause trouble. If the suspicious person turns out to be simply lost,ill, confused, or new to the neighborhood confronting the person won't help;and if he is a criminal confronting him may trigger a violent reaction.
Don't tease mean dogs ;keep them in sight and call the dog-catcher to deal with them.
“I beg to differ;Neighborhood Watch is just that :watch,it is not about questioning suspicious people.”
You don’t have to be neighborhood watch to ask suspicious people what they are up to. Anyone can, and should. You can’t force them to answer, but if they don’t it’s a pretty good indication that it’s time to call the police on them. So many indifferent, uncaring, or downright cowardly people in the world. It’s the reason criminals feel like they can get away with anything. Too many only care about themselves.