Edison has been watching too many After-School Specials. He thinks anyone else on the street is there to abduct him and he has to scare them off. He does so by barking "Stranger!" very loudly for all to hear.
We've been trying to explain to him that he is fine as long as he's with us.
Luckily, he seems to be understanding as his stranger bubble has gotten a bit bigger - now it isn't every person/dog/bicycle in a 2 block radius.