When I was a spy listening to phone calls in Berlin, we used "u/i" for "unidentified"; "B-val" (B-value) for stuff we were pretty sure of, "C-Val" for stuff we were not so sure of.
"Unident" works for me, but u/i is easier. I like the B-val, C-val stuff for classifying guesses. Transcribing folk songs by ear is often like listening to phone calls and trying to make out what people are saying.
-Joe Offer-