A mark by which the goods or services of any applicant for registration may be distinguished from the goods or services of others shall not be registered if it:
provided, that nothing in this subdivision (5) shall prevent the registration of a mark used by the applicant which has become distinctive of the applicant's goods or services. The secretary may accept as evidence that the mark has become distinctive, as used on or in connection with the applicant's goods or services, proof of continuous use thereof as a mark by the applicant in this state for the five (5) years before the date on which the claim of distinctiveness is made; or