Individual contact with no text notification signal

[AC Question]

I never get a notification when i have received a text from this single contact; message is accompanied by the "no sound" symbol: horn with a slash through it. How do I turn it back on?

 

[NerdgrlApps]

Try this (for Android 4.4): open "messaging", click on the conversation for the contact, hold menu button to get the menu and choose "Chat Settings" then press the "..." menu this gives an option which says "Restore default settings" - it will remove the mute and the mute icon.