Illegal Limousine Solicitation

I was taking a cab during my last trip and saw this notice on the taxi door (click to enbiggen). I understand the first three items (Compliment? Lost Property? Complaint?), but it's that third one that confuses me (Illegal Limousine Solicitation?). Maybe I'm just not the target demographic for such actions, but I've never once had anyone pull me aside and say "Psst! Hey buddy. You're not a cop are you? Want a limo ride?" Is this such a problem in America's cities that they actually have to create a hotline for it? And keep in mind that this sign is inside the vehicle, so by the time you read it, it is too late. Because there is nothing worse than someone offering you a ride in an opulent vehicle thereby making you the envy of everyone around.