The Hammer is a plain blunt melee tool, the kind of thing you grab when there is nothing better within reach. It has no brand and no real-world model to point to beyond being a hammer. Useful for quiet, close work or a quick improvised weapon, but you will trade up as soon as a firearm shows up.
As a melee tool, the Hammer is the kind of item you find lying around the world rather than buy. Rockstar has not shown exactly where it appears, so treat world pickups as the expected route for now.
The community companion for Grand Theft Auto VI. Database, maps, guides and tools for Vice City and the state of Leonida.