Keep a list of all of your serial numbers. WHile you can "report" a weapon as stolen, it can't get entered into the big national file of stolen guns unless you have the serial number.
Seriously, I was just talking to an ATF agent the other day, and she made the comment that a "responsible" gun owner (and the agent included herself) always kees a serial number list of all of their weapons. I can not begin to tell you how many dirtbags I have encountered with stolen weapons, but the guns weren't reported as stolen becuase the owner didn't know the darned serial number. It takes a couple of months to do a trace on a weapon, and I usually wind u talking to Joe Gunowner who says "Yeah, my pistol got stolen two years ago in a burglary, but I didn't know the serial number." The dirtbag will still get charged with the stolen gun, but most of the time they have already disappeared when you finally get the warrant three months later.
Keep a list of all of serial numbers for anything expensive, not just guns. Engrave your Driver's License number (not your SSN) prominenetly in at least two places on every item of property that you own that is worth more than $25. That is basic crime prevention, and about the only way you will ever get any of your proerty back if it is stolen. And before I get flamed, I am not suggesting putting your DL # on your guns, but I have done it to magazines.