"Mute" icon to the right of the contact name in messages

[AC Question]

For some reason two of the people in my messages have a mute symbol to the right of their name and I can't figure out what it is or how to turn it off. Any help would be much appreciated.

 

[King James4]

I'm having the same problem as well I with my Samsung Galaxy 6 but the only thing I can see is that all the contacts have iphones nothing else to figure out how to remove it or what causes it