Old sign about black stuff men ignored, passing remarks (10)
'passing remarks' is the definition.
(remarks made after someone has passed)
'old sign about black stuff men' is the wordplay.
'old' becomes 'o' (common abbreviation eg in OE for Old English).
'sign' becomes 'aries' (star sign).
'about' is a charade indicator (letters next to each other).
'black stuff men' becomes 'bitu' (I am not sure about this - if you are sure you should believe this answer much more).
'aries' put after 'bitu' is 'bituaries'.
'ignored' is the link.
I am not very happy about this link. It may belong to another bit of the clue.
Can you help me to learn more?
(Another definition for obituaries that I've seen is "late notices".)