I just listened to the EC121 recordings of Israeli helicopter pilots
approaching the Liberty after the attack. (All in Hebrew of course).

The pilot is asking whether the ship is dangerous and is been answered
that its not known whether the ship is dangerous or not and that he
should try to identify it.
Then the pilot notice an inscription "GTR 5" and asks if that means
something.

What is this "GTR 5" inscription on the ship?

thanks