Prying cigarette butts out of sidewalk cracks on the west side of the square this morning, I noticed this triangular bronze marker embedded in the sidewalk in front of what now is Rob Johansen's building but started life during 1867 as the T.A. Matson building, then was renovated and given its current stone Richardson Romanesque facade during 1915 by the Stantons.
Anyhow, this is a form of permanent advertisement for the American Luxfer Prism Co., purveyors of "Luxfer Prisms for lighting buildings with daylight."
These small squares of prism glass were installed in a wide full-width transom panel atop the street-level business facade of the newly renovated Stanton Buiilding. It's still there, behind boarding. There once were (and many remain although obscured) similar installations in many buildings around the square.
The theory was, prism glass picked up daylight and then reflected it deep into stores, thus reducing the need for reliance on artificial lighting. The suggestion here, too, is that the sidewalk (still in good shape) is nearly a century old.
Next time you're walking around the square in the neighborhood of the Stanton Building, keep looking down --- at least for a little while.