So long, notice that is for all to see (5)
I believe the answer is:
Here is my best explanation:
'so long' is the definition.
('adieu' can be a synonym of 'so long')
'notice that is for all to see' is the subsidiary indication.
'notice' becomes 'ad'.
'that is' becomes 'ie' ('i.e.' can be a synonym of 'that is').
'for all to see' becomes 'u' (universal dvd certificate).
(Other definitions for adieu that I've seen before include "Farewell, ami!", "Parting greeting", "See you later", "Au revoir (to a kind friend?)", "Fare thee well!", "Farewell (French)", "Gallic goodbye", "Ciao, in French", "Goodbye, monsieur" and "Goodbye, madame".)