The most common and most likely answer to this crossword clue is the 7 plus 4 letter word WAKE-UP CALL
I've seen this crossword clue in The Times
W
A
K
E
-
U
P
C
A
L
L
More clues leading to the result WAKE-UP CALL
Buddy explains!

The straight part
We know that "Notice" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case notice = wake-up call.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.