The purpose of a security seal is to ensure that no one has tampered with the contents inside your container. A great use of these is for your luggage and bags. For instance, use them to make sure no one has gotten into your luggage at the airport.
The key to using seals is to use one that is tamper-proof, or in reality, is very difficult to tamper with without you knowing. Almost every type of seal on the planet has been successfully breached and then resealed. Many folks use a form of seal on letters, to ensure no one has opened the letter before the intended party opens it first. There are many ways to remove these seals, inspect the contents, and then reseal the letter or box back up again. So what you can do is to get the best seal that you can, that is reasonable in cost. You can buy seals in Wal-Mart, and on the internet. Most of these can easily be broken and then resealed without you knowing. What you need is a higher quality seal, with serial numbers that cannot be purchased by someone else.
For instance, if you buy your seal at Wal-Mart, or a cheap internet store, they will be mass produced items with no serial number on them, or a serial number that is repeated and your robber can buy also. He will simply look at yours, and get one exactly like it, with matching numbers and all. So what you need to do is find a better quality seal, with non-repeating numbers, and use only those. These seals are not expensive; they just require you to be informed and choosy on which ones you buy.
http://www.amazon.com/Stanton-Concepts-PrivaSeal-Tamper-Indicative/dp/B004I0D1E0 These are good ones to use, sold by Security Snobs, and are only $6 for 20 of them! You don’t have to spend a bunch of money, just know that you need them and use them. You may be surprised how much better things go for you regarding your travels. No more stolen items. I use these on all my bags when I fly, and I take a picture of my bag, with the seal, number showing, at the airport. So if I get to my destination and my bag was tampered with or opened, I can easily prove it right there on the spot.