Hi,
Are you seeing these lines in inbox->workflow section OR inbox->documents where all notifications go ?
The username with 'US' at the start must be coming from some of your workflow to your user decison/action task (through binding) where you are displaying it. Check in your workflow what is the source of username with 'US' i.e. how it is being filled in your worflow container. if he is the approver which you are determining from some activity step in workflow (before user decision step), then create one more container element in workflow and fill it with user name without 'US' from the same user determination activity. then you can use that workflow container and bind it to your user action activity type.
Regards,
Ibrahim