Sign on after trouble with guest (7)
I believe the answer is:
gesture
'sign' is the definition.
(I know that gesture is a is a more specific form of the action of sign)
'on after trouble with guest' is the wordplay.
I cannot quite understand how this works, but
'on' could be 're' ('on' can be mean 'with reference to') and 're' is found in the answer.
an anagram of 'guest' is 'gestu' which is present in the answer.
This accounts for all the letters.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for gesture that I've seen before include "Hand movement to communicate" , "Eg, shrug or wave" , "A physical motion or signal" , "Expressive arm movement" , "Significant movement" .)