Are you talking legally, or in the eyes of Poseidon?

Legally, there's no requirement for vessels in Maryland that I know of.

If you have a vessel documented with the Coast Guard, the name is registered and must appear on the boat according to regulations.

The boat must be at least 27 feet in length or be commercial to be eligable for being documented.

So, the only things you have to abide by is your personal taste and making sure Poseidon is happy.

In general, just start calling the boat what you want to call it, paint the name on or not.

Poseidon may see through that and give you bad luck, so do the research and find one of the many ceremonies people have come up with to appease. And be careful the name you choose so as not invite the bad luck (or scorn...).