Dash perhaps part of GP's email address? (4)
I believe the answer is:
sign
This clue is a quadruple definition!!
'dash perhaps' is the first definition.
(dash is a kind of sign)
'part' is the second definition.
(sign is a kind of part)
'of' acts as a link.
'gp's email' is the third definition.
The answer and definition can be both related to communication as well as being singular nouns.
Maybe there's an association between them I don't understand?
'address?' is the fourth definition.
(address is a kind of sign)
Can you help me to learn more?
(Other definitions for sign that I've seen before include "Mark" , "Communicate silently" , "As the star was for 14 across" , "Omen or indication" , "Public notice; gesture" .)