The only evidence of a refusal to accept, or of a resignation of the office of President or Vice President, shall be an instrument in writing, declaring the same, and subscribed by the person refusing to accept or resigning, as the case may be, and delivered into the office of the Secretary of State.
Structure US Code
CHAPTER 1— PRESIDENTIAL ELECTIONS AND VACANCIES
§ 1. Time of appointing electors
§ 4. Vacancies in electoral college
§ 5. Certificate of ascertainment of appointment of electors
§ 7. Meeting and vote of electors
§ 9. Certificates of votes for President and Vice President
§ 10. Sealing and endorsing certificates
§ 11. Transmission of certificates by electors
§ 13. Same; demand on district judge for certificate
§ 15. Counting electoral votes in Congress
§ 16. Same; seats for officers and Members of two Houses in joint session
§ 17. Same; limit of debate in each House
§ 18. Same; parliamentary procedure at joint session
§ 19. Vacancy in offices of both President and Vice President; officers eligible to act