a northern irish version of "ya mum".
The normal reply to it would be "aye, yer's ma's ma"
or "smell yer ma"
mind you, the conversation ( if you could call it that) could also start with smell yer ma, depending on what mood you're in.
me - "yer ma"
you - "yer ma's ma"
me - " aye, smell yer ma"
and so on...