Pretty much all boats have decals on them. They are used to display the name of the boat or boat number.
If your boat has a fiberglass hull, then I strongly recommend not to use a metal razor blade as its easy to damage the surface.
The other method also used to remove decals is a heat gun or hair dryer. Now I would suggest that this technique is fine for cars and trucks, though with boats and a fiberglass hull, I caution against this method.
The reason is that heat can affect fiberglass in an unusual way.
The steps to follow to remove the decal are
1) Use a plastic razor blade (so the surface is not damaged) such as Wonder Blade to lift the edge of the decal
2) Once you have lifted the edge of the decal, slowly push the decal along to remove the whole decal
3) Use some Eucalyptus oil to remove any adhesive left on the surface
4) Wash clean with tap water so the surface is like new