Which of the following is classified as a prohibited offensive weapon?

A machine gun is classified as a prohibited offensive weapon due to its capability to fire multiple rounds in rapid succession with a single trigger pull, which places it in a different regulatory category compared to standard firearms. The law in Pennsylvania specifies certain firearms that can be classified as offensive weapons based on their design and the threat they pose to public safety.

The other options, while they may be controlled or regulated, do not fall under the same category as machine guns in terms of being outright prohibited. Handguns and shoulder stock rifles can be legally owned and used in many situations, given they comply with applicable laws and regulations. The volunteer police baton, intended for use by law enforcement in specific circumstances, also does not carry the same risk profile as a machine gun and is typically allowed under local laws.