They Do It Like That

WOW Insider has produced a nice list of tell-tale signs you can use to determine the spec of another player without using the Armory. In addition, Mike has provided a quick run-down of what each spec can and can’t do. Although most players are probably familiar with the nuances of their own class(es), this guide might provide some insight for those that have no clue about other classes.

I’ve reproduced the Hunter section here (for obvious reasons). Check out “A spec guide for classes that aren’t yours” at WOW Insider.

Hunter Specs

Beast Mastery (a.k.a BM)
How to Spot: Their pet is gigantic and red. This is a result of Bestial Wrath, a talent that temp buffs their pet when used. You’ll also see a Ferocious Inspiration buff show up on you when grouped with them– it ups your damage when the pet scores a crit.
They Can: Kill stuff with their pet– a BM Hunter’s pet is a killing machine, not least because of Intimidation, a talent that allows the pet to actually stun its target for a few seconds. They can also solo like no one else– a BM Hunter might be the best solo class in the game.
They Can’t: Raid quite as well as other Hunters– since most of their strength is in the pet, and their pet doesn’t do well under AoE (which lots of raid bosses use), they’re at a disadvantage in groups.

Marksmanship
How to Spot: Trueshot Aura is the best tell– it’s a groupwide buff that ups your Attack Power. Silencing Shot and Scatter Shot (man I hate Scatter Shot– it disorients you for a few seconds) are also Marks Hunters only.
They Can: Break out the ranged DPS. Unlike BM Hunters, their power is in their ranged attacks, which makes this a nice class for PvP, although abilities like Silencing Shot and Scatter Shot work well in raiding situations also.
They Can’t: Do much to you if you close into their dead zone or melee range. They can shoot you down, but if you survive their barrage, their bag of tricks consists of trapping you until they can get to range again.

Survival
How to Spot: Survival is probably the most unpopular Hunter spec, since it has lots of melee-related abilities (and it’s for a class you’d be crazy to melee with). Still, since the expansion, Survival has gained a lot of ground in raiding, especially with Expose Weakness, a shot that increases attack power against the target for the whole raid.
They Can: Do crowd control. Nobody does Hunter CC better than Survival Hunters, since their traps all get boosts.
They Can’t: Do any of the other cool stuff that Hunters can do– frankly, the Survival tree needs work.