Back of his uniform says police. Secret Service don't wear that.Secret Service snipers, and agents, have the discretion to shoot at will when they see a threat. They do not "call it in" to the head of the Agency. They take the shot.
And Secret Service has jurisdiction over local police. So it is conceivable that a local cop would need authorization to pull the trigger.
Also, in his post, he never says that he is Secret Service.
Only the Shadow knows.