The most common and most likely answer to this crossword clue is the 10 letter word NEUTRALITY
I've seen this crossword clue in The Guardian
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Buddy explains!
The straight part
We know that "It’s a Swiss hallmark" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case it’s a swiss hallmark = neutrality.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 NEUTRALITY mean?
NEUTRALITY noun- The state or quality of being neutral; the condition of being unengaged in contests between others; state of taking no part on either side.
- Indifference in quality; a state neither very good nor bad.
- : The quality or state of being neutral.
- The condition of a nation or government which refrains from taking part, directly or indirectly, in a war between other powers.
- Those who are neutral; a combination of neutral powers or states.