The most common and most likely answer to this crossword clue is the 7 letter word ENSIGNS
I've seen this crossword clue in The Guardian
E
N
S
I
G
N
S
More clues leading to the result ENSIGNS
- Head off plans adopting new standards
- Bottom halves of paving stones damaged square flags
- Sensing changes in standards
- Men having abandoned male faults, accepting good standards
- Standards dean occasionally ratifies
- Junior officers, they climb the mast
- Jacks drunk Guinness when out of uniform
- Sensing slipping standards
Buddy explains!

The straight part
We know that "Jacks" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case jacks = ensigns.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 ENSIGNS mean?
ENSIGNS noun- A badge of office, rank, or power.
- The lowest grade of commissioned officer in the United States Navy, junior to a lieutenant junior grade.
- A flag or banner carried by military units; a standard or color/colour.
- The principal flag or banner flown by a ship (usually at the stern) to indicate nationality.
- Any prominent flag or banner.
- A junior commissioned officer in the 18th and 19th centuries whose duty was to carry the unit's ensign.
- To designate as by an ensign.
- To distinguish by a mark or ornament.
- To distinguish by an ornament, especially by a crown.