Communications biology has been built on the advantages of signal clarity. One gets the best insight into the character of this phenomenon by studying social paraphernalia. Though much social ornamentation strengthens the signals being transmitted, there is an equally large portion of ornamentation which obscures the signal or falsifies it in some way. Because of its greater unknowns and hence potential for disadvantageous social experience, a signal stripped of direct personal involvement is often a more potent display than otherwise. Such a signal contains less information but enough to raise expectations.
People often write letters to strangers, whom they plan to visit, for reasons of social strategy.
But the absence of personal involvement makes them threats. Joe Blow walking in the door unheralded may be merely a derelict who has lost his way. I can imagine it is akin to that formal letter of introduction, or the glance at an engraved calling card. The flame of self-doubt burns higher on a lean mixture of little information and lots of imagination. The gestures of an animal meeting a strange of his kind are cautious.