Here’s a cryptic one from the east side of North Hayford Avenue between Fernwood and Saginaw. It’s the only one like it I’ve seen. I initially took it to read “HW” but on closer inspection I think it is “RW.” The style reminds me a little of the BWL stamps.

A name with two letters doesn’t give me much to go on. There is an RW Concrete Sawing out of Dorr, but they describe their main lines of business as “Concrete Breaking, Sawing & Drilling.” In other words, they are all about deconstructing concrete, not constructing it. Dorr is also a good hike away, though not an implausible one.