Mark signalling about daughter in top hat (5)
I believe the answer is:
tilde
'mark' is the definition.
(tilde is a kind of mark)
'signalling about daughter in top hat' is the wordplay.
'signalling about' becomes 't' (I am not sure about this - if you are sure you should believe this answer much more).
'daughter' becomes 'd'.
'in' indicates putting letters inside.
'top' means to remove the first letter.
'hat' becomes 'tile' (I've seen this before).
'tile' with its first letter taken off is 'ile'.
'd' placed into 'ile' is 'ilde'.
't'+'ilde'='TILDE'
Can you help me to learn more?
(Other definitions for tilde that I've seen before include "part of Sao Paulo, originally" , "Sign on Spanish character" , "Diacritical mark over a letter thus, n" , "Accent on some Spanish words" , "Squiggly mark" .)