Marked? Indeed not! (7)
I believe the answer is:
denoted
'marked? indeed' is the definition.
The definition and answer can be both to do with communicating as well as being past participle verbs.
Maybe there's an association between them I don't understand?
'not' is the wordplay.
I cannot really see how this works, but
'not' could be 'no' (negative) and 'no' is located in the answer.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for denoted that I've seen before include "Indicated or meant" , "Signified" .)