Here’s a first so far: two stamps on the same slab, facing opposite directions. This is on the west side of North Hayford Avenue between Fernwood and Vine.

It’s difficult to read in the photo, but based on the several others on this block of Hayford (all 1960) I know that it says J.A. Johnson.

I didn’t notice any other doubled up stamps on this block, even though there are several other J.A. Johnson stamps. My guess is that their practice was to stamp the beginning and end of a run of sidewalk paving, and this was a solo block so they stamped both sides. It makes sense to me, anyway.