Service tax applicability on t/o less than 10,00,000

Dear Members;

If the Proprietorship firm, have taken a Service Tax Registration Number recently for the providing Man-power services to the Private limited comapny and Partnership Firm under the RCM basis.

I need to know whether such proprietorship firm need to add service tax number in the Invoice isssue by them, even though they have not crossed the Turnover of Rs. 10,00,000 .
As the service provided by this Proprietorship firm is on RCM Basis, then also they can take the benfit of Rs.10,00,000 basic exemption from charging service tax.

Please guide..

Thank you