Spooner's hurriedly left disreputable paper, seeing sign of danger (3,4)
I believe the answer is:
red flag
'sign of danger' is the definition.
'red flag' can be an answer for 'sign' (I have seen 'Sign of trouble' mean 'red flag' so perhaps 'sign' could also mean 'red flag'). I also know that 'danger' relates to this answer.
'spooner's hurriedly left disreputable paper' is the wordplay.
I cannot quite understand how this works, but
'left' could be 'red' (red can informally mean communist) and 'red' is found within the answer.
The remaining letters 'flag' is a valid word which might be clued in a way I don't see.
This explanation may well be incorrect...
'seeing' is the link.
Can you help me to learn more?
(Other definitions for red flag that I've seen before include "Socialist banner?" , "Banner used to signal danger - or communism" , "Emblem of socialism" , "A flyer" , "Song and symbol of socialism" .)