Md. Code, Public Safety § 5-703

(a) (1) A person may not purchase, receive, sell, offer to sell, or transfer an unfinished frame or receiver unless it is required by federal law to be, and has been, imprinted with a serial number by a federally licensed firearms manufacturer or federally licensed firearms importer in compliance with all federal laws and regulations applicable to the manufacture and import of firearms.

(2) Except as provided in paragraph (1) of this subsection, a person may not sell, offer to sell, or transfer a firearm unless it is imprinted with a serial number as described under subsection (b) of this section.

(b) (1) This subsection does not apply to:

(i) possession of a firearm unless a person knew or reasonably should have known that the firearm was not imprinted with a serial number as described under this subsection;

(ii) possession of a firearm that does not comply with the marking requirements described under this subsection by a person who received the firearm through inheritance, and is not otherwise prohibited from possessing the firearm, for a period not exceeding 30 days after inheriting the firearm; or

(iii) possession of an unfinished frame or receiver by a person that made or manufactured the unfinished frame or receiver, without the use of any prefabricated parts, and who is not otherwise prohibited from possessing the unfinished frame or receiver, for a period not exceeding 30 days after the person made or manufactured the unfinished frame or receiver.

(2) On or after March 1, 2023, a person may not possess a firearm unless:

(i) the firearm is required by federal law to be, and has been, imprinted by a federally licensed firearms manufacturer, federally licensed firearms importer, or other federal licensee authorized to provide marking services, with a serial number in compliance with all federal laws and regulations applicable to the manufacture and import of firearms; or

(ii) the firearm:

1. has been imprinted by a federally licensed firearms dealer, federal firearms manufacturer, or other federal licensee authorized to provide marking services, with:

A. the zip code of the current owner or person that made, completed, or initially assembled the firearm;

B. the initials of the current owner or person that made, completed, or initially assembled the firearm; and

C. a number that does not match a number used by the current owner on another firearm or by the person who made, completed, or initially assembled the firearm on any other firearm that the person has made, completed, or initially assembled; and

2. has been registered with the Secretary.

(c) (1) A person who violates subsection (a) of this section is guilty of a felony and on conviction is subject to imprisonment not exceeding 5 years or a fine not exceeding $10,000 or both.

(2) A person who violates subsection (b) of this section is guilty of a misdemeanor and on conviction is subject to imprisonment not exceeding 2 years or a fine not exceeding $10,000 or both.

(3) Each violation of this section is a separate crime.

(d) A federally licensed firearms dealer or other federal licensee authorized to provide marking services who imprints a firearm under subsection (b)(2)(ii) of this section shall imprint the firearm in compliance with all federal laws and regulations applicable to affixing serial numbers to firearms, including:

(1) minimum size and depth requirements; and

(2) requirements that the numbers not be readily susceptible to being obliterated, altered, or removed.