In its appearance the Dignity appears to be a yacht styled boat from which the player can undertake the scuba diving activity. It is not known yet whether it will be drivable or not.
It is possible that Michael owns a Dignity, since in his trailer, his daughter can be seen partying with friends on the same boat.
Interestingly the bollards on the rear of the boat are shaped like the "V" of GTA V.
The name of the boat is a joke on the fact that is an exclusive boat for "people with dignity".
The name "Dignity" perhaps pays homage to the song of the same name by Scottish band Deacon Blue. The song's subject is about a man who is saving to buy a boat with the intention of calling it Dignity.