The most common and most likely answer to this crossword clue is the 8 letter word APPROVER
I've seen this crossword clue in The Daily Telegraph
A
P
P
R
O
V
E
R
Buddy explains!
The straight part
We know that "one showing signs of appreciation" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case one showing signs of appreciation = approver.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 APPROVER mean?
APPROVER noun- One who approves or gives approval.
- In English common law, a person who accuses a confederate; one who commits approvement.