absence of revenue stamp

 I think, it may come under 'deficit stamp'.  Hence it can be properly stamped by the collector of stamps by imposing costs. Apart from this, an unstamped or less stamped document, may not be used as a primary evidence, but it can be used as secondary evidence.

In your case, devoid of stamp, the document loses it status from primary evidence, but it can be used as secondary evidence.

I am a renowned Advocate & Solicitor, having had speciality in stamps & registration laws. While agreeing with the earlier view of Mr. Murali, you can also affix revenue stamp aside the signature and cancell the same by drawing two parallal lines across the revenue stamp.    H. M. BHAGAT  2.9.08