At the bottom of the stats page there is a section titled Nearby ADS-B Sites. I think the nearest 20 are listed. Of these four, maybe five have the username in bold type.
What is the significance of the users listed in bold print?
It’s the people who are showing their names instead of an online username. (whatever they typed in as their first name and last name)
In your account settings section 3 (“FlightAware Community Features”) you can choose to show or not show your real name.
This is site-wide, not just on the stats.
Thank you.
Also related to this section: I have two sites, one in .uk and one in .nl. For the .uk one, I see myself in this nearby section. For the .nl one however, I do not. 
Is there a per-site privacy setting somewhere that I am not aware of? I’ve compared all the settings on this same page (map precision, site coordinates, etc) and from what I can tell they do match (and for both sites they do indeed seem to show other folks in the area).
Is this functionality maybe not working well for people with multiple and somewhat distributed sites?