This is the devil of all registrations in proprietorship. Since, you don't have any registration, you think this is registration for proprietorship firm.Right? Wrong!
It is registration for Service Tax which means even if service tax is not applicable, you need to file nil Service Tax return (Half yearly).
Service Providers, beware. Service Tax Registration is not mandatory unless you touch Rs 9 lakhs as your annual turnover (Period from 1st April to 31st March next year).
You don't have to pay Service tax if your Annual Turnover is less than Rs 10 lakhs.