Cryptic crossword clue
Marshal notices seats occupied by 1,000 holders of these? 6,7

The most common and most likely answer to this crossword clue is the 6 plus 7 letter word SEASON TICKETS

I've seen this crossword clue in The Guardian
S
E
A
S
O
N
T
I
C
K
E
T
S

Buddy explains!

The straight part
We know that "these" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case these = season tickets.
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.

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