With the badges you should only be treated as a policeman if you are either awarded the badge, or have a high enough speech and/or charisma to convince people.
As far as 'artie' goes. IMO, any artillery or other large crew served weapons should only be usable by factions (player or NPC) and should be extremely costly to transport and operate. You would have to use a team of brahmin to transport 'artie', would have to have a team that actually knew how to operate it, would have to have forward observers to call in the coords, and, of course, the ammunition itself (a 155mm howitzer round costs roughly $1000).
'Artie' should be something a faction only uses in the most dire situations. If it costs $1000 a round in our world, i'd hate to see the equivalent costs after armegeddon.
Of course, that's all in regards to realism for the most part, which is relatively moot in most any game world. But, to be portrayed in any believable fashion, artillery would be incredibly powerful and there would have to be a LOT of restrictions on it's use due to how powerful it is. Of course, there could be various artillery, from mortars to howitzers, with different restrictions accordingly.