Mr. Zimmerman holds a concealed weapon permit issued from the State of Florida. He is authorized to carry the weapon in a concealed manner wherever Florida Statute dictates. Neighborhood Watch programs are designed for members of a neighborhood to be eyes and ears for police and to watch out for their neighbors. They are not members of the Police Department, nor are they vigilantes. Training provided by law enforcement agencies to Neighborhood Watch organizations stresses non-contact surveillance of suspicious situations and notifying police of those situations so that law enforcement can respond and take control of the situation.
Mr. Zimmerman was not acting outside the legal boundaries of Florida Statute by carrying his weapon when this incident occurred. He was in fact on a personal errand in his vehicle when he observed Mr. Martin in the community and called the Sanford Police Department.
Whatever handgun he carries is not "registered," There is no provision for such registration in FL, and no public records of the gun are kept other than records of the gun shop on their possession of it until transfer of the piece after background check of the purchaser; purchaser's identity erased a few days after transfer.
M was, as a minor, a person prohibited from public carry or handling of a DW except (I believe) on a recognized firing range and under the direct supervision of a person not prohibited. Long guns not classes as DW, I suppose. AFIK
My guess is that since Z was not operating under color of law enforcement, the police dispatcher would not give him, a private citizen, a direct order to cease and desist; but would more likely request that he refrain from direct involvement and wait for police intervention. Which, of course, he could ignore. IMHO.
Thanks for your factual piece of the puzzle!