Stamp theft, despite the scare stories that you sometimes hear, is really not much of a problem. We rarely have a customer inform us that his stamps were stolen and the APS’s stamp theft committee almost never sends out an advisory of a stolen collection. In the 1970’s stamp theft was more of an issue than it is now and the change from stamps being an actively stolen commodity to an infrequently pilfered one tells us a lot about the changes in our hobby and our world in the last thirty or forty years.
The reason for the reduction of stamp thefts is threefold. First, stamps have languished in value so that on a “value to difficulty of fencing ratio” they are an inefficient product to steal.  High end TVs, computers and jewelry have made much more appealing targets over the last thirty years and stamps that are stolen are often taken as an afterthought of another robbery. Second, most criminals like the easy and big money and that money is in drugs. One could make the case that the only good byproduct of the drug war is that by criminalizing drugs and enormously raising their price, you attract the criminal element to the drug business and have kept most types of property safe from the small percentage of people who prefer crime to work. And lastly, the Internet has made images of most stamps that you have bought in the last fifteen years a permanent part of the world record. This has dramatically reduced the sales value of stolen stamps because they can’t be listed on the Internet as they would be recognized and a trail would lead back to the thieves.
Still, you see stories of how careful you need to be about stamp theft. Most of this is just illusion. The APS insurance groups insures stamps against fire or theft for 0.3% of the declared value per year. That is $150 per year for a $50,000 stamp collection. For this they write and administer the policy, and insure against water, fire and theft (and make a profit). Based on these insurance rates its hard to believe that you have much to worry about with your stamps. You should still have insurance but also you can have peace of mind.