The most common and most likely answer to this crossword clue is the 7 letter word VIEWERS
I've seen this crossword clue in The Times
V
I
E
W
E
R
S
Buddy explains!

The straight part
We know that "They can see" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case they can see = viewers.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 VIEWERS mean?
VIEWERS noun- Someone who views a spectacle; an onlooker or spectator.
- Someone who watches television.
- Any optical device used to view photographic slides.
- A program that displays the contents of a file.
- The manager of a colliery, who directs its workings and ventilation.