2.41—Proof of distinctiveness under section 2(f).
(a)
When registration is sought of a mark which would be unregistrable by reason of section 2(e) of the Act but which is said by applicant to have become distinctive in commerce of the goods or services set forth in the application, applicant may, in support of registrability, submit with the application, or in response to a request for evidence or to a refusal to register, affidavits, or declarations in accordance with § 2.20, depositions, or other appropriate evidence showing duration, extent and nature of use in commerce and advertising expenditures in connection therewith (identifying types of media and attaching typical advertisements), and affidavits, or declarations in accordance with § 2.20, letters or statements from the trade or public, or both, or other appropriate evidence tending to show that the mark distinguishes such goods or services.
(b)
In appropriate cases, ownership of one or more prior registrations on the Principal Register or under the Act of 1905 of the same mark may be accepted as prima facie evidence of distinctiveness. Also, if the mark is said to have become distinctive of applicant's goods by reason of substantially exclusive and continuous use in commerce thereof by applicant for the five years before the date on which the claim of distinctiveness is made, a showing by way of statements which are verified or which include declarations in accordance with § 2.20, in the application may, in appropriate cases, be accepted as prima facie evidence of distinctiveness. In each of these situations, however, further evidence may be required.