Can I determine whether a user in a user field is a user of the app?

If the user is a registered user, a proper name will appear. If you see an email address in the users field, that particular user has not registered under that email address.

Hi Chris,
Thanks for the quick reply.  Your solution would tell me whether the user was a Quick Base user, but I need to determine whether the user is a user of the application.  For example, they may have access to apps A, B, and C, but this is app D.  I want the formula to tell me that this user doesn't have access to this app.

Hi Chris,

Unfortunately, there is not a formula function to call whether a user in the field has permissions in the current application. To store more information on a user that can then be called down into other tables in the past I have used a Resources or Employees table that has a record for each user that I can then add information to. You can even populate/update it by exporting your current User table as a CSV and then Importing in user name, role, and any other info you want from that CSV right into the Resources table. Then you can have a formula field that checks each user's role and if there role isn't set to none they are a user in the app. 

Once I have that Resources table set up to track the user, their role, and their status of being an active user or not I make the user field in my Resources table the key field and then I can match it to any other table I want via a Relationship and the existing user field or another field set up to mirror the user picked in a field. It does change the application up a bit and requires some groundwork but does allow for storing info on whether a user is active in the app or their current role, etc. I hope this suggestion is helpful Chris.