The most common and most likely answer to this crossword clue is the 7 plus 5 letter word SWAGGER STICK
I've seen this crossword clue in Financial Times
S
W
A
G
G
E
R
S
T
I
C
K
More clues leading to the result SWAGGER STICK
Buddy explains!
The straight part
We know that "Staff seen on the square" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case staff seen on the square = swagger stick.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.