I don't think I've ever seen a "Stop" sign like this before... but some of you have, and recognized that it's a stop sign for the trolley car... (thanks Steve!)

 That PCC (Presidents’ Conference Committee) streetcar/tram is on Pittsburgh's No. 13 (Emsworth) route on Center Ave., just about to cross North St. That route was in operation from at least 1915 to September 3, 1966.

https://www.jalopyjournal.com/forum/threads/vintage-shots-from-days-gone-by.428585/page-6058#post-12925181