In order to prove that he is a seasonal worker, the employed person covered by Article 1 (c) of the Regulation shall be required to submit his contract of employment stamped by the employment services of the Member State in whose territory he has gone to work or has worked. If no seasonal employment contract is concluded in that Member State, the institution of the country of employment shall, where appropriate, issue, in the case of a claim for benefits, a certificate attesting that, on the basis of information supplied by the person concerned, the work which he is doing or has done is of a seasonal nature.