I use double dashes – like this, a lot.
I’m not that distinctive. But I think if there’s any habit I have, it’s simply popping into a thread to say “Hey this reminds me of a funny joke/website/flash animation, so even though it’s a bit off-topic, I’m going to provide a link.”
Hmm, I don’t think there’s anything much, but maybe I talk a little too much about ME and I’m argumentative, often for no reason.
But then, that could be so many of us. 
(Crikey, that’s it! My usage of would give me away!)
The proper way to indicate actions is, of course, double colons
::indicates the proper way to indicate an action::
The IRC-derived /me is also correct, but less common:
/me explains that this is also a correct way to show action
I’ve used both asterisks and colons. The problem with colons is that they can produce unwanted smileys.
Writing an “oops I forgot to mention” post - another quirk. This is such a post: A.) how could I forget a favorite sitcom reference, and 2.) how come I haven’t been using it much lately.
Start
sometimes, I just quote posts, turn them purple, and throw out a catchphrase.
I think mine would be one of three things, ok four:
[ul]
[li] An absolute love of lists, spoiler boxes, and all the little toys on the SDMB.[/li][li] Use of this fellow: 
[/li][li] Writing my post halfway through and completely forgetting my original point,[/li][li] And posting something and quickly coming back and posting again because I’d remembered my original post.[/li][/ul]
Other than that, you guys would have to tell me.
And your sweetness & light would give you away every time…
I don’t use internet abbreviations. I don’t think anyone would notice that, though. It’s kind of like proving a negative, if you know what I mean.
I suppose it’s a tossup between wit, wisdom, and badinage.
Then again, it is also possible that my tendency to indulge my verbosity with the dreaded run-on sentence, that convoluted, recursive, near-impenetrable morass of voluble verbiage, cascading clauses, proliferating punctuation, meandering modifiers, and – far too often – over-abundant alliteration, rambling or sometimes lurching along a perilous path of but tenuous connections with the original thought which prompted the peripatetic excursion into logorrhea – if such a term is apropos to describe an affliction more appropriately associated with the spoken word – might catch the eye of a passing moderator, pique the interest of an administrator already far too well-acquainted with the quirks, follies, and foibles of my writing style, might set to ringing a tiny bell in the consciousness of some erudite Doper who, recognizing a pernicious pattern of prose composition, would then ponder the possibilities, ruminate upon the recherche – or, to be more accurate, perhaps, recondite – rodomontade of the suspect poster; who would then heed the call of those mystic chords of memory declaring the true identity underlying the tantalizingly familiar tone of some neophyte Doper’s fledgling contributions to the discourse of this cyber-community; who upon coming to a well-reasoned conclusion as to the well-known face behind the unknown mask would then test that hypothesis by tossing up conversational balls abounding with topics – cats, horses, science fiction, to name just three – upon which that keen-eyed sleuth had observed your (not so) humble servant to wax eloquent in the past; and upon eliciting responses very much in the vein of the typical ETF bloviation, would then call down upon the scurrilous sock’s head the great and terrible wrath of the Powers That Be.
Or maybe it’d be the smilies. :eek: :dubious: 
:smack:
Ditto.
I have none. You couldn’t pick my posts out of a lineup of similar posts. After all, lots of people flirt, use smilies, and say silly things.
I post pantsless.
So that’s where ‘/me’ comes from! Whenever I’ve seen it on here I’ve assumed it was a typo of /em.
Having never taken to IRC but played on MUDs and MMORPGs (EQ, EQ2, CoH) I’m only familiar with /em - short for ‘emote’. What’s /me short for?
Anyway, back on topic: emotes in asterisks sigh or prefixed with /em (or even just /) are another giveaway that I’m posting.
One interesting thing I’ve found in this thread is that reading some of the other people’s quirks, I could be a sock*****. I’m interchangeable with at least two other posters in terms of writing style. On any other board I’d say my tendency to play Devil’s Advocate was a notable trait - but on the SDMB it’s scarcely unique.
*****posterisnotasock.
Pointless? Looks about 24 point to me.