The most common and most likely answer to this crossword clue is the 8 letter word UNTITLED
I've seen this crossword clue in The Sunday Telegraph
U
N
T
I
T
L
E
D
More clues leading to the result UNTITLED
Buddy explains!

The straight part
We know that "Non-specific way to label painting/common?" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case non-specific way to label painting/common? = untitled.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 UNTITLED mean?
UNTITLED adjective- Having no title.