What does a “crossed out bell” icon mean in messaging?

One of my contacts has a "bell that’s crossed out" beside it in "Messaging" text messages list… what does this mean?
BELL-CROSSED-OUT ICON_MESSAGING.png
See below:

2021 FEB 20_MESSAGES-QUES.png

Attached Images

• 2021 FEB 20_MESSAGES-QUES.png (32.0 KB)
• BELL-CROSSED-OUT ICON_MESSAGING.png (1.3 KB)