Ubuntu Mate panel

[Richard Kimber]

I have a small question about Mate panel. On my panel there is an
inactive area where neither left nor right mouse clicking does
anything.  The area is not blank, however, and contains the characters
↕,9,A each in a circle, thus:-

http://www.nonplacet.co.uk/NON/19a.png

Can anyone tell me what the significance of these characters is? On
one occasion the 'A' and its circle turned red briefly. Presumably they
are indicators of something or other.  I can't seem to delete them, so I
may as well find out what they mean :)

I'm using Ubuntu Mate 16.04.3 LTS
-- 
Richard Kimber