The most common and most likely answer to this crossword clue is the 9 letter word INCOGNITO
I've seen this crossword clue in Independent
I
N
C
O
G
N
I
T
O
More clues leading to the result INCOGNITO
- Popular icon got dressed up in disguise
- Noticing nothing strange in disguise
- Criminal coming into money, initially hiding false ID
- Disguised in company – go outside idiot!
- Noticing outrageously surprised cry’s disguised
- Secret of gin and tonic? Mix with love
- Minor worker, fool in number following one with identity concealed
- Cognition misinterpreted as something else
- Noticing changes by Oscar, under an assumed name
- Nameless doctor noticing ring
Buddy explains!

The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does INCOGNITO mean?
INCOGNITO noun- One unknown or in disguise, or under an assumed character or name.
- The assumption of disguise or of a feigned character; the state of being in disguise or not recognized.
- Without being known; in disguise; in an assumed character, or under an assumed title.
- Without revealing one's identity.