Thank you so much for your suggestion, though that is not exactly what I am looking for.
If I got it right, you are looking for some sort of tool/script that will show you if the VM is backed up. First thing to note is that Veeam does not install anything inside VM (unless you use Veeam Agents
to backup VMs) so there is nothing like file or registry key to look for. The only sign that some VM is backed up is the fact that it is added to an existing backup job and the job throws no errors. As Vitaly's said, there is a reporting tool
that provides you with a complete overview of VMs that have/haven't been added to backup jobs.
If for some reason you don't want to use the abovementioned report, please feel free to search in this subforum
for a script that will provide you with a list of VMs that are added into a job. Please also consider looking at built-in notification options