HB, your dealer is misinformed.
Please see Chapter 6, "Making NFA Firearms by Nonlicensees" and also reference chapter 7, "Manufacturing NFA Firearms":
All NFA firearms must be identified by a serial number and other specified markings95. If an existing
firearm is being used in the making of the NFA weapon, and that firearm is serialized, the existing serial
number should be used (unless it duplicates a serial number already used by the maker on Form 1) and
entered in Block 4(g). If the weapon is of new manufacture, the applicant must assign a unique serial
number and enter it in Block 4(g). For example, a unique serial number could be composed of at least 4
digits preceded by the initials of the maker. NOTE: alpha characters, e.g., a name, will not be accepted
as a serial number. If a name is to be used, there must be at least one numeric character in addition to
the alpha characters.
The serial number must be engraved or stamped on the receiver of the firearm and the caliber, model,
and identification of the maker must be engraved on the barrel or frame or receiver of the weapon.96 The
marking and identification requirements for a maker are the same as for a manufacturer. Refer to
section 7.4 for a detailed discussion of the requirements.
7.4.2 Additional information. Certain additional information must also be conspicuously placed on
the frame, receiver, or barrel of the firearm by engraving, casting, stamping (impressing), that is, they
must be placed in such a manner that they are wholly unobstructed from plain view. For firearms
manufactured on or after January 30, 2002, this information must be to a minimum depth of .003 inch.
The additional information includes:
(1) The model, if such designation has been made;
(2) The caliber or gauge;
(3) The manufacturer’s name (or recognized abbreviation); and
(4) The city and State (or recognized abbreviation) where the manufacturer maintains its place
To recap, when you (or your trust) fill out a Form 1 to make a new NFA firearm, YOU (or your trust) are the maker of that item. Per the current NFA handbook from ATF, the marking requirements for a maker are the same as those for a manufacturer. So yes, Virginia, you DO have to engrave or stamp your name (or that of your trust), city, and state abbreviation on the firearm.