Mark called around to entertain this writer (7)
I believe the answer is:
cedilla
'mark' is the definition.
(I have seen 'Diacritical mark ' mean 'cedilla' so perhaps 'mark' could also mean 'cedilla')
'called around to entertain this writer' is the wordplay.
'around' indicates an anagram.
'to entertain' means one lot of letters goes inside another.
'this writer' becomes 'i' (the person who is writing these clues).
'called' with letters rearranged gives 'cedlla'.
'cedlla' enclosing 'i' is 'CEDILLA'.
(Other definitions for cedilla that I've seen before include "mark not seen in 18 [FACADE]?" , "Mark indicating a softened consonant" , "Sign to soften C" , "Mark suggesting a 'c' should be pronounced an 's'" , "Mark, in foreign language" .)