Noticed about diamonds (3)
I believe the answer is:
ice
'diamonds' is the definition.
(slang term for diamonds)
'noticed about' is the wordplay.
'about' indicates the answer is hidden within the clue (the clue goes around or about the answer).
'ICE' can be found hidden inside 'noticed'.
(Other definitions for ice that I've seen before include "Cubes in a drink" , "It's cold and slippy" , "Frozen liquid" , "Rocks on which drink is served?" , "Solid H2O" .)