The most common and most likely answer to this crossword clue is the 8 letter word SALTIRES
I've seen this crossword clue in The Daily Telegraph
S
A
L
T
I
R
E
S
Buddy explains!

The straight part
We know that "Crosses" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case crosses = saltires.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 SALTIRES mean?
SALTIRES noun- An ordinary (geometric design) in the shape of an X. It usually occupies the entire field in which it is placed.
- The Saint Andrew's cross, the flag of Scotland.