Legal, since my Chinese HT Motor was politely left un-marked with any info about the size of the motor...but WE all know that it's over 49cc...
I'll tell you - I've got no issues with the cops around here. I wave to them, they wave back, everyone's happy. I think they like to see me on the bike with a real helmet, to be honest. Most cops are out there to bust balls on car drivers...hand out lots of tickets...but for us "pedestrians", I think they just don't want to have to scrape us off of the road, so if we look like we're trying to be safe, they have better things to do with their time.
I ride on the sidewalk doing a brisk 20mph down our main road (3 lanes, median, 3 more lanes) and when they see me there, I think they're glad I'm not holding back the 60mph cars. (Limit is 45, but hey, we're in Florida!)