The most common and most likely answer to this crossword clue is the 5 letter word BRACK
B
R
A
C
K
More clues leading to the result BRACK
Buddy explains!

The straight part
We know that "Fabric mark" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case fabric mark = brack.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 BRACK mean?
BRACK noun- Salty or brackish water.
- An opening caused by the parting of a solid body; a crack or breach.
- A flaw in cloth.
- Barmbrack.