You are required to monitor the amount you earned yourself and, still as per the licensing terms you really should read at this point, update to the license in the 14 days that follow the moment you reach the income limit.
Scirra still has a monitoring eye on things as well, but this is indeed not publicly discussed.
And moreover business laws also ask of companies and money-making individuals to use valid softwares in compliance with the terms of the company which publishes them.
So consider the authorities of your country as another monitoring eye.