Event Observer on the orders grid if someone selects an order and uses one of the actions in the drop down menu items

If someone selects and order by checking the box and then using one of the action items in the dropdown. I would like to add the user and timestamp and the action item they selected to the comments section of that order. Primarily just for auditing purposes.

Is there a module out there that does this already or no? If anyone could point me in the direction to start which event do i need to hook into with my observer that would be great. Need a bit of help getting this started.