Indication; authorise (4)
I believe the answer is:
sign
I believe this clue is a double definition.
'indication' is the first definition.
(I know that indication can be written as sign)
'authorise' is the second definition.
(I know that sign is a type of formalize)
(Other definitions for sign that I've seen before include "Authorise with a name" , "Communicate to the deaf" , "Traffic control - to write one's name" , "Omen or indication" , "Leo, for instance" .)