https://nationalfile.com/fbi-promises-to-hunt-down-anyone-who-lies-about-taking-covid-vax-as-vaccine-passports-loom/

This is the pertinent code which FBI is citing to convict you with a fine or imprisonment or both:

18 U.S. Code § 1017 - Government seals wrongfully used and instruments wrongfully sealed

Whoever fraudulently or wrongfully affixes or impresses the seal of any department or agency of the United States, to or upon any certificate, instrument, commission, document, or paper or with knowledge of its fraudulent character, with wrongful or fraudulent intent, uses, buys, procures, sells, or transfers to another any such certificate, instrument, commission, document, or paper, to which or upon which said seal has been so fraudulently affixed or impressed, shall be fined under this title or** imprisoned not more than five years, or both.** (June 25, 1948, ch. 645, 62 Stat. 753; Pub. L. 103–322, title XXXIII, § 330016(1)(K), Sept. 13, 1994, 108 Stat. 2147.)