The most common and most likely answer to this crossword clue is the 9 plus 6 letter word REVERSING LIGHTS
I've seen this crossword clue in Financial Times
R
E
V
E
R
S
I
N
G
L
I
G
H
T
S
Buddy explains!
The straight part
We know that "Warning signs given here" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case warning signs given here = reversing lights.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.