What does the tray icon represent?
 

I have looked through the inline help, but I can't find anything that tells you what it is and what the circles that change colour mean.

The colors changing represent the status of your searches. When a light is green, the search is active, if it is blinking, it is active and new results have been returned that you have not yet seen. Purple means that no search is active. The circles correspond to the searches as below:
Top right - Search 1

Bottom Left - Search 2

Bottom Right - Search 3

Hope that helps.

Shaun