InstantSSL will accept different kinds of documentation from each type of organization as proof of its right to use that organizational name. Your "proof of org name document" needs to be official, and needs to be independently verifiable. For example, if you are claiming to be "XYZ, Inc." then you should produce a certificate of incorporation from your Secretary of State that proves that you have been registered in your state under that name.

Most organizations fall into one of the following categories:

Companies, Corporations, Incorporations Inc, (Pty) Ltd., Plc., B.V., S.A. GmbH, LLC, State issued Trademarks, etc.
We will need a copy of an official city, state, or country document, articles of incorporation, or a DUNS number in your state and country. These documents can be faxed.

Partnerships
You should be registered with national, state or local authorities. Please provide us with a copy of some form of verifiable proof of the partnership name.
DBA's and Fictitious/Assumed Names
DBA ("Doing Business As") or Assumed/Fictitious names will need to send a copy of your DBA registration papers. Any other official city, state, or country documents will generally be sufficient, as long as we can cross check with the relevant authority.
Government Departments
We require an original signed letter from the head of that department on the appropriate letterhead, along with contact information for his or her office and immediate superiors.
NGO's (Non-Government Organizations)
We require an original signed letter from the Chief Executive, Chairman or Managing Director of the NGO, on the appropriate letterhead.
Universities and University Departments
We will require an original signed letter from the Dean or Vice-Chancellor responsible for that department. Note that this must be on the appropriate letterhead, accompanied by contact information for the University concerned.
Special Interest Groups
We will issue such groups with certificates but request that you contact us first to discuss verification and authentication details.

Private Individuals and Proprietorships [for non-US customers only]
If you want a certificate but are not registered, incorporated or licensed to do business in your area, we can issue a certificate to you in your personal capacity using your name as the organization name. Please note that we only do this on rare occasions under special circumstances. In order for us to issue a certificate to you, we will need the following:
A photocopy of your passport/identity document or driver's license, notarised or certified by a relevant authority in the country where you live. The person certifying this documentation needs to provide their name and telephone number for further confirmation if necessary. Please post the original copy to the InstantSSL representative you chose during the application process.
A copy of a valid, current bank statement in your name (you may black out your financial details) OR a valid, voided check from your bank account.
If you are a sole proprietor, we may ask you to also send documents from the department of revenue such as VAT registration certificates.
Please make sure to send us the correct documentation the first time around. This will ensure that your request is verified in good time and your certificate issued in a timely fashion If you have any questions, please contact your local office or representative before generating your certificate request and before submitting any documentation to Thawte.

What if I am Different?
If you believe you have a right to use an organizational name but you do not fit into the categories described above, please contact your nearest InstantSSL representative to discuss your situation.