Damn.
Anyways, a USMS loadout would be very simple.
I won't cover their anti-drug/mexico jurisdiction setups, just their plainclothes enforcement one. They make for an awesome law-enforcement loadout, for a number of reasons.
Firstly, they're cheap, mostly civvy stuff and the odd assault vest. The guns are all fairly standard. Also, they're hard as nuts. When you see the FBI charge into a massive druglab or whatever in all their bullet proof gear in shows like Fringe, that's not what the FBI do, that's the USMS, the FBI then casually walk in once the USMS have put bullets into everything.
Clothing wise, during research, I've found a lot of them wear blue jeans, a t-shirt, some sort of trucker cap, boots of any kind and sunglasses (dark ballistic glasses for us). They then simply wear an assault vest with two patches "USMS" and "Police", one front, one back, no real etiquette for which is which. They also tend to stick to drop leg holsters.
Guns?
M4A1, RIS if you want it, no lasers usually, but a red dot (aimpoint) and a barrel mounted torch are standard. Crane stocks feature less than normal sliders. Any long shotgun, Glock pistols (usually the G17) and that just about covers it.
Real easy loadout if you want to do something a bit different with a law enforcement twinge, but not the usual SWAT, CO19 sort of thing...