Hi Selva,
You have good documentation on this here which explains ur basic query.
Digital Signature - SAP Solution Manager - SAP Library
further i have seen this used mainly pharma companies so that authorized users can set status to RELEASED or final version etc as per customer use case scenario.
authorization object is below which controls the user to digitally signed it
C_SIGN - SAP Solution Manager - Security and Authorizations - SCN Wiki
a good how to
UC00019 - SAP Solution Manager - Security and Authorizations - SCN Wiki
hope this resolves
Thanks
Prakhar
