Anyone is free to make a complaint on a sign, with or without a website. This seems to be a site dedicated to New York (?) signs – mostly wallscapes.
I don’t advocate getting involved in illegal signs in the first place, since they are a lot of work for little benefit – you normally get caught within a couple years and have to tear them down, and you can never really sell the structures. People are attracted to illegal wallscapes since they can often get their money back in the first 6 months or so, and then everything between then and when they come down is profit.
If you own legal signs, then you would applaud this type of site as it removes your illegal competition.
The moral is just to stick with legal signs.