Thanks for posting these photos, johnny g. Brings back a lot of memories for me, as I grew up in this vicinity of Hackensack.
When I was quite young, the stretch of road between Essex St. and Standish Ave. used to be called just Prospect Ave. If I’m recalling correctly, the road was renamed “S. Prospect Ave” probably sometime in the early 1950s. I remember when the name change happened, as we had an elderly neighbor who was griping about having to change his mailing address.
New street signs were then installed to reflect the name change. From the weathered condition of the street sign in your photos, it seems possible that it is the original street sign from that era.