Daniel I don't know actually, but I think they should have their ways of doing it. And if I am not wrong this TV/radio license bill is being paid together with your property tax so they might be able to come for that purpose ( property tax) and check from there.
But then again I think we are looking at a figure of S$110/year. Under 10 bucks a year. This ( according to a message on their bill) is for running and producing educational programmes for our kids that are screened in the afternoons where no income ( or minimal ) is coming in from ads etc.