From Princelaw.com:

So, ATF, trying to be cute and find a way to require NICS checks without Congressional action, declared trusts not to fit the definition of a “person” under the GCA. No big deal, especially for us in Pennsylvania, as Pennsylvania Instant Check System (PICS) checks are already required for all NFA firearms, except silencers. But, not so quick…let’s look at Section 922(o) of the Gun Control Act…

Section 922(o) provides:

(1) Except as provided in paragraph (2), it shall be unlawful for any person to transfer or possess a machinegun.
(2) This subsection does not apply with respect to–
(A) a transfer to or by, or possession by or under the authority of, the United States or any department or agency thereof or a State, or a department, agency, or political subdivision thereof; or
(B) any lawful transfer or lawful possession of a machinegun that was lawfully possessed before the date this subsection takes effect.