Revenue Stamp!!!!!!

Hello to all

In which act or regulation is it required to sign on revenue stamp when a payment is given to someone. Normally i have seen these small denomination ( 25/50 paise) on rent receipts, wages register, insurance premium payments(LIC/National Insurance etc).

On which kind of payment it is required to sign on it?

Is there any threshold limit  say Rs.500/- upto which no payment is to be sign on revenue stamp?

Could anyone provide the exact name or link(URL) of related act/regulation?

Thanks