The most common and most likely answer to this crossword clue is the 4 letter word NATO
I've seen this crossword clue in The Times
N
A
T
O
More clues leading to the result NATO
- It's formed by a group of signatories?
- Military alliance in collision at once
- Group of countries taking part in a tournament
- What’s spread evenly among UN: parts of alliance
- Initiate nuclear attack, taking out alliance
- They keep the peace in sanatorium
- Security group must contribute to plan at once
- A ton transported around for military group
- Not a bad defense alliance
- Security organisation negative about cover for airport
Buddy explains!

The straight part
We know that "It's formed by a group of signatories?" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case it's formed by a group of signatories? = nato.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 NATO mean?
NATO noun- A tree of the genus Mora
- The wood of such trees