If it was a “real” sign it would be mounted eight feet up in the air, pointed along the curb rather than parallel to it, and would be difficult and expensive to get installed.
Instead, this private sign is conveniently mounted 3-4′ above the sidewalk, directly facing the car that might park illegally on the bike lane. In short, it’s actually useful.
In this particular instance, there is a curb side bike lane and a popular restuarant adjacent. Legal on-street parking commences just a few metres further west, so motorists must try to “squeeze in” one last car and then block the bike lane. This sign is thus a community-sensitive effort on behalf of both motorists and cyclists.