Thanks for that et_and_family, however, I appear to have made my usual mistake of not giving nearly enough information.
I have Windows 10, and that pops up notifications from the action bar of running or finished backups in the bottom right of the screen. In order to turn this off, I open the Notifications Menu, click 'All Settings', 'System', 'Notifications and Actions', and scroll down.
When I scroll down, I see multiple versions of 'Macrium Reflect Disk Imaging and Backup', all but the latest of which are set to 'off', these previously disabled notifications I assume have been uninstalled/upgraded, and left behind the old Notification, which is just a black box.
The only one that is enabled is the one with the Macrium logo. Again I'm assuming this is after an upgrade where the previous version is left un-linked so the icon is black.
It's easy enough to turn it off again, but it appears I've done this four times already.