Would you have a tattoo done? Our sister site WoW Insider has, in the past, posted about people having tattoos of various World of Warcraft symbols done. I sport a tattoo myself, and I've certainly considered getting a WoW tattoo done. Tattooing is certainly an extreme, and fairly permanent, way of professing your love for a game, so I suppose that might be 'too far' right there.
You could go for a simpler option, and pick up some of the nifty official merchandise available for various games instead.
I doubt you'll be surprised to hear that there is a veritable plehtora of merchandise available for WoW. There's the pen and paper RPG, (which I have but can't find anyone willing to indulge me an take part in my campaign) the TCG with its many tasty loot cards, and there's the wearable merchandise. Why not grab yourself a T-shirt or two – my personal favourite is the Camp Taurajo one. Wear one of these around town during downtime and see how many "For the Horde!" or "Grab your sword and fight the Horde!" cries you can hear being thrown your way. I wouldn't bet much on the latter though, to be honest. Sorry Mike.
If your place of work has a 'dress down' day in effect, declaring your allegiance for the entire cafeteria to see may unearth a fellow WoW player you never knew was there.
While merchandise for some of the other MMOs appears to be thin on the ground, it is out there. The official Square Enix store has a plethora of Final Fantasy merchandise of course, but specific Final Fantasy XI merchandise is a little thinner on the ground. You can pick up a ring or keyring for whichever kingdom you've pitched your flag to. Failing that, don't fight the cuteness and give in to a Baby Chocobo plushie.
SOE's Station.com store supplies hats, sweatshirts and few other bits and pieces for Everquest and Everquest 2, but not much else I'm afraid. And outside of one book published a few years back, Star Wars Galaxies merchandise seems to be non-existent.
Moving away from official merchandise and succumbing once more to the inevitable pull of WoW; you could try your hand at some home-made crafts.
Maureen Carter, over at WoW Insider regularly shares WoW-inspired crafts and recipes in her World of Warcrafts column. If you're like me and regularly burn cereal, culinary creations may not be the way to go. Level up your real-world crafting skills and try your hand at one of her craft projects. Everyone needs Healthstones, right?
Alternatively, if you are comfortable in the kitchen, head over WoW Insider anyway and have a look at the Well Fed Buff column, which has some interesting cuisine choices for you to try your hand at, then email me and tell me how to do it. Just be careful which recipe you try – Caf'd Macaroni and Cheese? Seriously Amanda, what were you thinking?
Then again, you may not even care about any of this stuff. None of my friends or colleagues plays WoW, or any other computer game. In fact, I think most of them consider me to be slightly daft for doing so. You however, may not be in the same boat, and you can yourself with sitting down and going over last night's raid/5-man/group quest with your friends, bemoaning the one piece of loot that refuses to drop, or consoling each other over the lousy DPS-er you had to PuG because your other friend had connection issues. Maybe that's enough for you, and that's just peachy. If not, and you like taking your love for your hobbies a little farther than most, then let us know what you've done to show it.