Spot the sack that's put on board (6)
I believe the answer is:
notice
I believe this clue is a triple definition!
'spot' is the first definition.
(I've seen this before)
'the sack' is the second definition.
(to give someone notice is to give them the sack)
'that's put on board' is the third definition.
(a notice is put on a noticeboard)
(Other definitions for notice that I've seen before include "This is usually given before quitting job" , "Detect" , "Announcement (of the sack?)" , "'Take heed of, perceive (6)'" , "Advance warning of job resignation" .)