It is a Nuka-Cola sign, now re-purposed as a devastating melee weapon. It consists of a partially functioning Nuka-Cola neon sign which is mounted on a pole with an electric cord wrapped around the top, and tape at the bottom. The weapon uses a self-contained power supply. It does bonus electrical damage when a Critical Hit occurs.
The critical electrical damage may come from the electrical wiring around the pole leading to the semi-functioning neon sign which keeps it self-sufficient. There isn't, however, any sign of why the electricity actually escapes upon a critical hit.
The Nuka Breaker was created as a nod to the 2011 fan-made short film and webseries Fallout: Nuka Break. The Fallout: Nuka Break team put the Nuka Breaker in episode 3 after seeing it in a pre-release screenshot of Gun Runners' Arsenal before they knew that Obsidian was referencing their series.
The Nuka Breaker was also featured briefly in the 5th and 6th episode of the second season of Nuka Break.
The overall design of the Nuka Breaker sign is similar to traditional neon Coca-Cola signs. The use of a stylized cursive for the word 'Nuka' and the bottle tilted next to it. The slogan itself "Take a Nuka Break!" is similar to an old Coca-Cola slogan "Pause...Drink Coca-Cola".
↑Zack Finfrock, lead actor of the fan-made short film and webseries Fallout: Nuka Break: "In a recent trip to Obsidian, we were luck enough to find out the sign was a nod to us. But we put it in the episode as a nod to them, before we knew that. It's all a big circle of nodding."