Not sure that this is actually going to change driver and car-door-opener behavior, but really appreciate that the city has seen fit to make an effort at education. Car doors and inattentive drivers could kill or maim a cyclist.
The sign is on Beacon Street westbound, just east of the Staples store (which is on the left in the video).
I saw this — a huge improvement over the sign placement on Centre St last year (in the bike lane).