The writing instrument favored by the former U.S. president is generally identified as a Sharpie marker. This preference became particularly visible during his time in office, specifically when signing official documents and executive orders.
Using a bold marker allows for a prominent and easily reproducible signature. The Sharpie, with its thick lines, provides a visually strong autograph suitable for high-profile occasions and public display. Historically, presidents have employed various pens for official acts, with some even distributing these pens as commemorative keepsakes after landmark legislation is signed.