Notices these people tend to be put in boxes (9)
I believe the answer is:
witnesses
'notices' is the definition.
The definition and answer can be both related to communication as well as being plural nouns.
Maybe they are linked in a way I don't understand?
'these people tend to be put in boxes' is the wordplay.
I cannot quite understand how this works, but
'to be' could be 'esse' (I've seen this in another clue) and 'esse' is found 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 witnesses that I've seen before include "They provide sworn testimony" , "Sees" , "Observers" , "They testify under oath in a court of law" .)