Although I have never run a Vampire game. I come from a time when Vampires were blood sucking fiends that were to be feared and destroyed - not seen as a tragic hero or role model (guess that's why I make such a great hunter). However, I thirve on realism in any game and below are just a couple of bullet points I have come up with playing in various other chapters:

1) Cardboard representation of items - Too often, I have seen people wearing leather biker jackets pull out of them M-60 machine guns to use in combat. My original thought was to carry an actual phys rep, but local law officials might have a problem with that. I borrowed something I saw at another game at a convention over a decade ago. Take a piece of card stock (the very stiff stuff that is often used for mounting or picture framing) and cut it into a square which the weapon could normally fit in. You don't want to cut a silhouette of a pistol - as in dark lighting, those look like real things to police officers. If such a square would have alot of 'extra room' in it (say as in the case of an AK-47) then make two squares and tape them together - one for the main gun, and one for the clip. To offset the use of various powers and skills (such as Obfuscate) allow the person carrying the weapon to be able to fold it a certain number of times (I would recommend no more than twice folded).

2) Limit in game police influence - I have watched massive battles take place on main streets, only to have the local Venture 'make a call' and it completely disappears from official records. And I have watched this happen night after night after night. If the vampires have no strong sway over local government, then they will be forced to be more careful about the Masquerade. Sheriffs and Scourges will have a much larger job on their hands but it will keep the feeling of the 'secret society' closer to the vest. After all, with about 3 cases of reported military hardware usage in a city, you'll soon have the National Guard in there - and what vampire wants that? Yes, a Venture's (or many vampires for that fact) main strength is his contacts. But unless he owns the entire police force, all the local newspapers as well as every citizen that might witness such an encounter, someone will eventually contact someone else outside of their influence and then all hell breaks loose. By stating in the beginning of the game that no character has any powerful sway over the local police, the players will keep their rampaging in check (or at least the Scourge will make sure their characters do).