What makes a person or a vehicle “suspicious?
What “suspicious” is, is a subjective decision on the part of the caller. Manner of dress, for example, may indicate a workman hired by a resident, while an actual burglar may be attired in a 3-piece-suit. A person apparently loitering for some length of time, peering into cars, on private property attempting to find concealment would be suspicious. It is up to the caller to make that decision, acting on the “better safe than sorry” principle.