What’s this icon?

[Pagemakers]

What’s this icon?

Only appears sometimes and only when the car is stopped.

Pressing it makes it change to a mute icon but nothing mutes as far and I can tell.

 

[Jeeves]

Proximity warning noises (referred to as chimes in the manual p 84).

 

[Pagemakers]

Thank you! Can’t say I’ve ever noticed the icon before.