Notice I intended to conceal Charlie's weight (12)
I believe the answer is:
Here is my best explanation:
'weight' is the definition.
(I've seen this before)
'notice i intended to conceal charlie's' is the wordplay.
'notice' becomes 'sign' (I've seen this before**).
'intended' becomes 'fiance' (I've seen this before).
'to conceal' means one lot of letters goes inside another.
'charlie' becomes 'c' (phonetic alphabet: alpha, bravo, charlie etc.).
'fiance' placed around 'c' is 'ficance'.
(Other definitions for significance that I've seen before include "Importance, meaning", "weight", "Import" and "Meaning".)