Just going by the
this example created by the FAA, it seems pretty clear that they want you to mark the actual aircraft
(and not a removable part of the aircraft).
If you take time to dig into the subject further, you'll likely find
this document which states you must "mark the aircraft in accordance with the provisions in 48.200 and 48.205".
14 CFR 48.205 states the following:
"The unique identifier must be affixed to the small unmanned aircraft by any means necessary to ensure that it will remain affixed for the duration of each operation."
You've been around here for a while now, so I'm sure you've seen cases where a prop or battery was nowhere to be found when a crashed drone was recovered. That being the case, it doesn't seem marking those parts would satisfy the must "remain affixed for the duration of each operation" requirement.