Leaving no room for doubt following every sign it’s OK (3,5)
I believe the answer is:
all clear
'sign it's ok' is the definition.
(signal shouted to show something is safe)
'leaving no room for doubt following every' is the wordplay.
'leaving no room for doubt' becomes 'clear' (I can't justify this - if you can you should give a lot more credence to this answer).
'following' says to put letters next to each other.
'every' becomes 'all' (similar in meaning).
'clear' after 'all' is 'ALL-CLEAR'.
Can you help me to learn more?
(Other definitions for all clear that I've seen before include "Permission to proceed" , "Signal that danger is past" , "Siren sound to signal end of air raid" , "ARP signal" , "with absolutely no ambiguity" .)