The most common and most likely answer to this crossword clue is the 4 plus 2 plus 3 plus 5 letter word SIGN OF THE TIMES
I've seen this crossword clue in The Times
S
I
G
N
O
F
T
H
E
T
I
M
E
S
Buddy explains!
The straight part
We know that "which shows a trend" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case which shows a trend = sign of the times.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.