Mark in bed in South East (8)
I believe the answer is:
inscribe
'mark' is the definition.
(thesaurus)
'in bed in south east' is the wordplay.
'bed' becomes 'crib' (I've seen this before).
'in' indicates putting letters inside.
'south east' becomes 'se'.
'crib' placed into 'se' is 'scribe'.
'in'+'scribe'='INSCRIBE'
(Other definitions for inscribe that I've seen before include "Engrave or write upon" , "Engrave; dedicate" , "Write or cut words into a surface" , "Engrave; enter (name in list)" , "Scratch" .)