While operating under Part 107, in what form must a remote pilot be able to present proof of aircraft registration if asked by the FAA or law enforcement?

Why →By statute, the operator must make the certificate of aircraft registration available for inspection when requested by a federal, state, or local law enforcement officer. The FAA accepts either a paper copy or an electronic copy, which is practical for small UAS where attaching a paper document to the aircraft is not feasible. The registration number must still be marked on the aircraft, but the marking does not replace the certificate.

The trap →The attached-paper option borrows from manned-aircraft habits, but a drone is too small to carry documents, which is exactly why an electronic copy is accepted. The serial-number-photo option confuses the external marking requirement with the separate requirement to make the registration certificate available for inspection.

Field note →Keep a photo or PDF of your registration certificate on your phone. That electronic copy is fully compliant and is the easiest way to satisfy an on-site request.