I work in a group within a NOC. Frequently we have a situation where someone has looked at an out of service node then someone else looks at it because it is not obvious that it has been looked at.
My thought is that we can change the dot to an upside down triangle when someone is working on it. This could be done through the current manage nodes interface so that a few nodes can be done together. This shape could be manually changed back to the current round or one of the other new shapes manually.
If there is a temporary outage due to weather or maintenance a right side up triangle could be set for a few hours but still monitor (red, yellow, green) so that we knew its' immediate status. This would change back to a circle based on a timer.
A square might be used for longer maintenance like a vendor waiting on parts. This would be manually changed back when the event was cleared.
If it was possible to add some information like the name of who was doing the work or a comment like weather/power/upgrade in progress that would be an enhancement.
I could see other users using these symbols for other reasons. The visual identifier will provide immediate value.