Endless, asinine rubbish about Instagram symbol (8)
I believe the answer is:
insignia
'symbol' is the definition.
(insignia is a kind of symbol)
'endless asinine rubbish about' is the wordplay.
'endless asinine rubbish' becomes 'insigni' (I am not sure about this - if you are sure you should believe this answer much more).
'about' becomes 'a' (abbreviation in Chambers).
'insigni'+'a'='INSIGNIA'
'instagram' 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?
(Other definitions for insignia that I've seen before include "Badges of office" , "arms" , "Stars and stripes, say" , "Badge of membership" , "marks" .)