Ok, well rare in the sense that this type of installation isn't really commonplace nowadays. The current preferred method being a single long mast arm for the approach that holds both thru and left signal heads.
Median pole mounted signals, or these "T" poles, are less popular in new installations. Particularly in cases like Myosh's 1st & 3rd StreetView examples with short/narrow median islands, such poles are very susceptible to vehicle strikes. I know of one intersection in Las Vegas where the left turn signals were pole mounted on the islands and multiple hits and replacements finally prompted the city to install a new mast arm to hold the left turn heads.