33 C.F.R. § 175.21
Condition; size and fit; approval marking
No person may use a recreational boat unless each PFD required by § 175.15 is—
(a) In serviceable condition as provided in § 175.23;
(b) Of an appropriate size and fit for the intended wearer, as marked on the approval label; and
(c) Legibly marked with its approval number, as specified in 46 CFR part 160.