@sanbornc If you are wanting to just find all computers that aren't assigned to anyone.. You could just set the Criteria with a "Username" is blank..
If you are wanting to check for specific users.. That may have to be a custom API script as an EA to set the variable of the current logged-in user, then read the username field and match against the variable of the current logged-in user.
Just throwing out ideas
Thanks @JustDeWon Im trying to find all USERS not computers, that are not assigned to someone. The end result here is to create a report of all the employees in our organization that don't have computers assigned to them. I have imported our company wide employee roster into JAMF and assigned employees to their computers. I just need a report of the employee's who dont have any computers assigned to them yet. In Users, it lists if a Computer is assigned to a user, I just a report that says this. I was going to make s Smart Group for this, then make it s Dashboard, but maybe there is a better way to do it?