Intimations, I see, in brief written messages (7)
I believe the answer is:
notices
'brief written messages' is the definition.
'notices' can be an answer for 'messages' (notice is a kind of message). I'm unsure of the 'brief written' bit.
'intimations i see in' is the wordplay.
'intimations' becomes 'notes' (I can't justify this - if you can you should believe this answer much more).
'see' becomes 'C' (the word for the letter, according to Chambers).
'in' indicates putting letters inside.
'i'+'c'='ic'
'notes' going around 'ic' is 'NOTICES'.
Can you help me to learn more?
(Other definitions for notices that I've seen before include "Perceives, sees" , "Posters; sees" , "Observes the public proclamations" , "Sees; adverts" , "Discovers" .)