The Remington Police models are shown on Remington's Law Enforcement site.
There's a link in the lower right-hand corner of the regular Remington site, or just go to:
http://www.remingtonle.com
Here's the actual differences between the 870 Espress and the 870 Police Model:
The Express Home Defense Model has:
A plastic trigger group.
The dimples in the mag tube and the new style magazine retention system.
A rougher finish inside and outside with some burrs left in place.
A rougher blue job.
A less polished bore.
A two piece barrel. (not 100% sure about this)
Hardwood or synthetic stock, with a sporting-length fore end.
An 18", cylinder bore barrel, with a bead sight.
Some Metal Injection Molded (MIM) parts, like the extractor.
The 870 Police has:
An aluminum trigger group.
The old style magazine retention system.
A much smoother finish inside and out, no burrs or rough edges.
A military-grade parkerized finish.
A polished bore.
A one piece barrel.
Walnut or synthetic stock, with a short police-length fore end.
Choices in different stocks, including Speed-feed, and others.
18" to 20" Improved Cylinder barrel, with a wide choice in sights, including rifle, ghost ring, and luminous.
Heavy-duty magazine spring.
Heavy-duty trigger-sear spring.
Sling swivel mounts.
No use of MIM parts, the extractor is milled.
The Express is a "budget" gun built specifically to cut costs so the Express can compete with the much cheaper to make Winchester and Mossberg guns.
The Police is esentualy a top of the line commercial Wingmaster with a tougher, dull finish.
It's MUCH better finished inside and out, and is a high end Cadallic to the Express's basic Chevy.