Catch sight of Mark (4)
I believe the answer is:
spot
I believe this is a double definition.
'catch sight of' is the first definition.
(to spot is to notice or catch sight of)
'mark' is the second definition.
(I know that spot is a type of mark)
(Other definitions for spot that I've seen before include "Small mark; see" , "Observe - place" , "Dirty blemish" , "See; pimple" , "point on snooker table" .)