Hummm...Boris
seems to me battery hatch to put "secret code" was but one suggestion describing an area that is easily accessible
there be some others you might consider easily accessible with no tools
What THEY said:
Methods to display aircraft identification: To ensure that the small unmanned aircraft can
be identified, the FAA will require that the unique identifier must be maintained in a condition
that is legible. The unique identifier must be affixed to the small unmanned aircraft by any
means necessary to ensure that it will remain affixed to the aircraft during routine handling and
all operating conditions.
For small unmanned aircraft registered under this part, the FAA does not specify a
particular surface upon which the unique identifier must be placed. Rather, recognizing
commenters’ concern about the small size of many of the small unmanned aircraft that must be
registered, the FAA simply requires that the unique identifier must be readily accessible and
visible upon inspection of the small unmanned aircraft.
In accordance with Task Force recommendations, a unique identifier is deemed readily
accessible if it can be accessed without the use of any tools (e.g., battery compartment). This
flexibility is expected to resolve the concerns of the television and motion picture industry and
preserve the authenticity of a replica if so desired, given that the unique identifier need not be
displayed on the exterior of the small unmanned aircraft.
Note please that Legible does not specify at what magnification...grin...
I think a micro dot anywhere on the exterior may satisfy brother Boris's need for stealth