How would you display these?

I would hang them! Or if you are doing assigned seats and not just tables then you can place them at their seat then have another sign letting people know what table they will be at.

We are doing assigned tables but not seats

I think you should hang them on something. People tend to be in a rush to find their seats, so the keys/tags that were nicely arranged on a table could definitely end up in a pile by the time a bunch of people have gotten to them, which would make it harder for everyone else to find their seats. I would use something like this to keep them nice and organized.