Representative sample of fake notices on X (5,7)
I believe the answer is:
cross section
'representative sample' is the definition.
(I've seen this before)
'fake notices on x' is the wordplay.
'fake' indicates an anagram (I've seen this in other clues).
'on' is a charade indicator (letters next to each other).
'x' becomes 'cross' (I've seen this before).
'notices' is an anagram of 'section'.
'section' put after 'cross' is 'CROSS-SECTION'.
'of' is the link.
(Other definitions for cross section that I've seen before include "formed when cut is implemented" , "Representative sample" , "Fair sample" , "Representative group" , "St Helena's "invention"?" .)