Most laptops (not all) have a small, rectangular slot for locking, called the K-slot; it'll look something like this:
http://upload.wikimedia.org/wikipedi...-lock-slot.jpg
To use it, you get a cable lock like this:
http://www.kensington.com/kensington...book-lock.aspx
This lock will obviously not stop someone determined to steal the laptop. What it _will_ do is keep hotel maids, college roommates, and coworkers honest.
http://stoptheft.com/site/products_security_plate.php <- I also had one of these on my laptop. I got a laptop in 2003 for grad school, but not being a student or needing a laptop anymore, I'm a desktop-only kind of guy right now.
When I go through the TSA with my tablet, I lock my backpack with a Master 630D non-TSA combination padlock. It locks the zippers tightly together, and while a box knife could make short work of the backpack, I use it to prevent TSA sleight-of-hand from making my property disappear.
The last time I went through the TSA with a laptop was in 2004--I put it by itself in a plastic tray, and Mrs. Mahohmei was on the other side to grab it. At this point in time, the TSA had not yet reached the eleventh circle of the underworld that they currently occupy.
If you're traveling alone with a laptop and have to open your TSA-friendly laptop bag, get that Kensington security cable and leash the laptop to something like a carrying handle on the laptop. This way, if a TSA clerk (or passenger, but most likely a TSA clerk) is going to steal the laptop, they have to take the entire bag, barring physically destroying the bag's handle right there on the spot. This isn't foolproof, but it'll make them look for an easier mark.
Today, given the TSA's theft record, if I had to travel with a laptop, I'd refuse to use anything _but_ a TSA-friendly laptop bag. There's no way on earth I'd leave my laptop, on a tray, where a TSA clerk could easily filch it.
http://www.tsa.gov/press/happenings/...rocedures.shtm
Laugh of the day: "Transportation Security Officers know what the inside of a computer should look like, and they can recognize irregularities."
This is the same TSA that caused someone to miss a flight because a MacBook Air didn't look laptoppy enough.