Signing a contract with popular ruler (6)
I believe the answer is:
inking
'signing a contract' is the definition.
'inking' can be an answer for 'signing' (inking is a kind of signing). I'm unsure of the 'a contract' bit.
'with popular ruler' is the wordplay.
'with' is a charade indicator (letters next to each other).
'popular' becomes 'in'.
'ruler' becomes 'king' (king is a kind of ruler).
'in'+'king' is 'INKING'.
Can you help me to learn more?
(Other definitions for inking that I've seen before include "Blackening" , "Wetting type for printing" .)