Weapons come in all shapes and sizes, I think trying to identify these through software would be difficult and you could end up with a lot of false positives, Hockey sticks for instance resemble the length and rough shape of a rifle.
Today the MV analytics are focused on anonymized human object/motion detection. There are other wishes and feature requests coming in, such as vehicle detection, and of course the API will grow and get enhanced with additional capabilities as well. For now, although there is no feature for this today, the MV team is listening and collecting data. Please make wishes as discussed, and more importantly discuss your use-cases with your Cisco Meraki team and they can get this feedback directly to the MV PM team, and inserted into a specific feature request.