Technically? I believe you should be in physical control of it. Realistically, unlikely to be an issue unless you're in a place with a state law that says suppressor possession is considered illegal until proven otherwise.
EDIT: For example here's what PA State Law looks like. They leave a pretty good exception in there for allowing the possession of what would otherwise be a "prohibited offensive weapon" if it is unlikely to be used unlawfully :
§ 908. Prohibited offensive weapons.
(a) Offense defined.--A person commits a misdemeanor of the first degree if, except as authorized by law, he makes repairs, sells, or otherwise deals in, uses, or possesses any offensive weapon.
(b) Exceptions.--
(1) It is a defense under this section for the defendant to prove by a preponderance of evidence that he possessed or dealt with the weapon solely as a curio or in a dramatic performance, or that, with the exception of a bomb, grenade or incendiary device, he complied with the National Firearms Act (26 U.S.C. § 5801 et seq.), or that he possessed it briefly in consequence of having found it or taken it from an aggressor, or under circumstances similarly negativing any intent or likelihood that the weapon would be used unlawfully.
(2) This section does not apply to police forensic firearms experts or police forensic firearms laboratories. Also exempt from this section are forensic firearms experts or forensic firearms laboratories operating in the ordinary course of business and engaged in lawful operation who notify in writing, on an annual basis, the chief or head of any police force or police department of a city, and, elsewhere, the sheriff of a county in which they are located, of the possession, type and use of offensive weapons.
(3) This section shall not apply to any person who makes, repairs, sells or otherwise deals in, uses or possesses any firearm for purposes not prohibited by the laws of this Commonwealth.
(c) Definitions.--As used in this section, the following words and phrases shall have the meanings given to them in this subsection:
"Firearm." Any weapon which is designed to or may readily be converted to expel any projectile by the action of an explosive or the frame or receiver of any such weapon.
"Offensive weapons." Any bomb, grenade, machine gun, sawed-off shotgun with a barrel less than 18 inches, firearm specially made or specially adapted for concealment or silent discharge, any blackjack, sandbag, metal knuckles, any stun gun, stun baton, taser or other electronic or electric weapon or other implement for the infliction of serious bodily injury which serves no common lawful purpose.
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