The most common and most likely answer to this crossword clue is the 2 plus 4 plus 2 letter word BE WISE TO
I've seen this crossword clue in The Guardian
B
E
W
I
S
E
T
O
More clues leading to the result BE WISE TO
Buddy explains!
The straight part
We know that "Appreciate/2" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case appreciate/2 = be wise to.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.