They are locks that can be opened by US Customs using a special key which in turn allows them to search your luggage if they consider it necessary. If you just lock your cases using standard locks (even those built in) they may simply break the locks in order to open your case. In addition to TSA padlocks you can also get luggage straps that are TSA compliant. They are available from virtually all shops that sell luggage (+ Boots, Superdrug etc) and can be found on those rotating stands where you find money belts, inflatable travel pillows etc. Alternatively, go onto ebay and just type in tsa to get an idea of what is available.
Or you could just use "cable ties" from your local DIY store and thread them through the zip fasteners of your cases . A packet costs coppers, made of plastic so customs cut them with ease if they wish to inspect. If they have inspected your case you just re-secure with the spares you had kept in your hand baggage.
A good idea Sailbad but not much use really as depending upon the airline, bags are either inspected in front of you after you've checked in [fine] or after you have headed for the departure gate in which case you can't re secure them.
I have just answered something similar which I think will be of interest to you. Look for my question [not a question but a warning] on this subject posted on 27th December and then scroll down the answers/enquiries to read my last contribution of a few mins. ago. Feel free to ask any thing not covered in that posting and I'll see if I can help.
We went on the Artemis 27 Dec - 10 Jan and we flew in to New Orleans. We used the TSA locks and our luggage was ok and had not been tampered with. Our friends were on the same flight and had the same locks but there luggage had been opened and checked. If they had just put on ordinairy padlocks
the locks eould have been broken off and the luggage could also have been damaged. We purchased the locks from one of our local department stores but later discovered that they were also on sale at a key cutting/shoe repair shop. So you should not have any trouble getting hold of them,.
I looked at TSA locks yesterday in Asda £6.50 but, on reading the label saw that they are mostly for USA. it enables security to inspect your luggage and relocking after. they use a code. Not yet having to have these for Europe I did not buy, hope I made the right choice.