How can you tell if it's a sidewalk?

An arterial street about a block from my condo was widened several years ago. At the time that it was rebuilt the specifications included a "sidewalk" on one side and a "trail" on the other. I assume that affects the rules for bicycling. I don't remember which side is the "trail" and it's not marked in any way that I can see. That's okay, however, because nobody seems to pay any attention.

FWIW, when I ride to the corner convenience store I ride on the sidewalk going to the store and I ride in the street with traffic coming home. That's so that I never have to cross the four traffic lanes.