Company Seal and Appointment Letters
The "common seal" of a company is not typically affixed to the appointment letters issued to employees. There are specific provisions where the common seal should be used, such as in the creation of charges for loans, shares, etc. However, what Prakash wants to know is about the rubber stamp of the authorized signatory who signed the appointment letter. Normally, no rubber stamp is affixed, but it is a good practice to do so. The designation or the words "Authorized Signatory" is a must whenever a rubber stamp is used (normally it's a... for ABC...& Co.. Name:_______ Designation:______ is a very ideal practice).
As others have said, anything can be faked. Nowadays, rubber stamp makers are given severe warnings that they should only accept orders for making rubber stamps from genuine parties whom they can identify. They should obtain the orders in writing on their letterheads, duly signed by a responsible official, and maintain/show them upon inspection. I have come across many makers who refuse to entertain orders from unknown persons. Of course, there are many exceptions too.
Prakash, if you have any doubt, you should contact them and ensure the authenticity.
Regards