When you receive or create a reservation with guest blacklisted by your property or who is on the Global Blacklist, you will see the reservation this way on BedView (red frame around the reservation):

And this way in the Reservation window (name and surname in red letters):

In Reservation window you can also see more information about the blacklisted guest:

In Blacklist you can see all guests blacklisted by your property:

When you create a reservation and the guest is on your Blacklist or in the Global Blacklist you will see two warnings with the information about blacklisted guest:

1. When you enter guest's name:

If the guest should not be blacklisted in your property (e.g. it is not the same guest), you can clear the information about the guest and enter it once again, without selecting the name written in red. 

2. When you save a new manually created reservation with blacklisted guest:

See also:

How to unblacklist guest?

How to blacklist guest?

How does the global blacklist work?