Motor vehicles are already banned from the sidewalk by traffic rules. There is no sign here saying "No murder" either, doesn't mean it's allowed. My city also specifically bans bicycles off the sidewalk too, but since a bicycle is defined in the code as having at least two wheels, unicycles are NOT included. This is settled court precedent here after some clown challenged the ticket he got for riding one and won. Rollerblading and skateboarding is fine.

Unless this city has specific laws banning bicycles/rollerblading/skateboarding, this sign has no legal power except as an advisory by the property owner. Ironically, violating this sign will be judged as tresspassing, not a traffic infraction. You are on the property at the invitation of the owner under presumption of following their rules. No follow = no invitation = tresspassing :(