The wedding gun was a device used by Demarchists in some of their wedding ceremonies.
Despite its name, it was a medical gadget with a handgun-like grip, rather than a weapon.
RS Glossary entry Edit
Wedding Gun: Device for implanting isotopically tagged neural material into the skull of a recipient.
- description from the official RS glossary 
- The wedding gun seems to be a more futuristic and pin-point accurate variation on real world jet injectors, sometimes also referred to as "injector guns".