Mark breaks into church (6)
I believe the answer is:
notice
'mark' is the definition.
('notice' can be a synonym of 'mark')
'breaks into church' is the wordplay.
'breaks' indicates anagramming the letters.
'church' becomes 'ce' (abbreviation for Church of England).
'into' anagrammed gives 'noti'.
'noti'+'ce'='NOTICE'
(Other definitions for notice that I've seen before include "Advance warning of an event" , "Sign posted in a public place" , "Observe, percieve" , "Become aware of; review" , "Announcement (of the sack?)" .)