Practical Airsoft Recommends:
Stargate S.G. 1 - Series 1
Stargate S.G. 1 - Series 2
Stargate S.G. 1 - Series 3
Stargate S.G. 1 - Series 4
Stargate S.G. 1 - Series 5
Stargate S.G. 1 - Series 6
On Dog Tags...
What is it about Dog Tags that MilSim players find useful?
OK, first off, MilSim, or Military Simulation, is a part of the Airsoft game that's growing weekly. Out go the half-hour spray-and-play games, where two sides charge at each other with wild abandon, using gratuitously large amounts of ammunition to, for examle, 'capture the flag'. In, comes more tactically themed games, that have a 'plot', and are more realistic (even gien the limited range of Airsoft models). The load-outs that players use are more 'military', they tnd to use camouflage and concealment, advance to contact, fire and manouevre, and other tactics more effectively, and even though there aren't that many fire fights in a typical MilSim game, they're altogether more adrenaline-packed, and exiting for the players. Like MilSim? I bloody love it! 
So, why am I mentioning MilSim, when the title mentions Dog Tags?
Easy. MilSimmers (that's what we're generically called, it seems!) tend to use military gear a lot more. Including Dog Tags, which are getting more and more popular, and not just in Airsoft. Think of them as a cheap medtag system, whereby if (God forbid) you're involved in a serious accident, a paramedic can see your tags, and note your details, without you having to be compos mentis to answer his "what's your name, mate?"!
Also, note that Dog Tags are an American system. The British Military use an Identity Disk system (metal for disk one, pressed fibre for disk two). The German military use a massive oval that snaps in two. I haven't a clue what other countries use, but it's probably similar to everyone else.
OK, get to the nitty-gritty! What goes on a dog tag?
There are five lines of text available on a military-standard Dog Tag. The firtst two usually relate to your name, the thord to your service number (I use my National Insurance Number, now I'm out of the Reserves), the fourth for your Blood group/type, the fifth for your religeon.
What lettering can I have on my tags?
Note that there's a maximum number of fourteen (14) characters that you can cram onto each line (including spaces, which each count as a letter):
Letters (all upper case): ABCDEFGHIJKLMNOPQRSTUVWXYZ
Numerals: 1234567890
Symbols: & ( ) - / ' , * @ + # ? = . £
OK, what about the second tag?
In the military, the second tag is a duplicate of the first. For civilian use, I have my next of kin details on the second tag (think worst ase scenario, OK?)
Here are a couple of images for your consideration, using the format I've noted above:
You can, of course, use any format you like, provided that there are a maximum of fourteen (14) characters per each of the five lines per tag.
Next up: where do I get them?
There a are a few sources in the UK, but probably the best is www.dog-tags.co.uk - they're reasonably prices, and part of Springfields Surplus, an established military surplus supplier in the north of England.
Enjoy!