I don't think you'd have to monitor it any more than you would monitor a business that puts up the rainbow flag on their window.
I think the key here is to make it voluntary and not push it on people or make it a top-down standard. Its absence should not imply racism. Perhaps the flair could located on another site where users of the shared economy list themselves as "diversity friendly". If you see a listing with the diversity "flair" and one of the reviewers is a person of color, you know that place is worth applying to as a person of color.
That would depend on what it was interpreted to mean by users. I can easily see AirBnB hosts being under pressure to display the flair for fear of being assumed racist otherwise and being boycotted by even white people who don't want to endorse racism. It might also make it easier for a person who feels discriminated against to sue (if they don't display when others are).
After all , you don't tend to see "blacks welcome" signs displayed at hotels, because that is the assumed default.
An easy solution to the problem would be to stop being a racist piece of shit, or else own up to it and accept the social consequences.
Another idea would be to have user ratings and feedback. I'm not sure if these services already do something like this, as I've never used them, but it could give hosts and drivers a means of rating their users so that they have some additional criteria by which to judge whether they want to loan their resources to a particular customer. That won't really solve the problem of new black customers who would have no prior rating, though. Maybe a criminal background check for customers is in order if people are really worried about being robbed or assaulted or some other nonsense. Of course that could cost time and money and could destroy the convenience factor of such services. A real bummer of a problem. I wish people were better.
I think the key here is to make it voluntary and not push it on people or make it a top-down standard. Its absence should not imply racism. Perhaps the flair could located on another site where users of the shared economy list themselves as "diversity friendly". If you see a listing with the diversity "flair" and one of the reviewers is a person of color, you know that place is worth applying to as a person of color.