This illegible stamp is on the north side of Elizabeth Street between Clemens and Fairview, just west of the alley. It doesn’t resemble any stamp that I recognize, but I can’t make out more than couple of letters. It looks to start with a K or B.

The date is also illegible. I can say with fair confidence that one digit is a “6”, but I can’t be sure whether it’s the last digit or the penultimate one, so I can’t even narrow down a decade.

Update 4/28/21: Walking past it in different light, it suddenly jumped out at me that it is an L. Ketchum stamp. The date is almost certainly 1960s, like the other one I’ve found, and I think it’s 1961.