Turning pro" is still the best answer--at least for me. And it helps to associate with other pros, whom we recognize if we ourselves are doing our work. As someone once said, "A gun recognizes another gun."
I've been a member of various writers' groups for more than fifteen years, and I can tell you it's true. Those who are serious about going pro recognize each other and frequently form alliances to the benefit of all, sharing craft tips, information about the business side of writing, and encouragement. Many such alliances (often critique groups) see member after member go on to achieve their goals.
So how does a gun recognize another gun?
1. Natural talent
This is critical. If there's not at least a native spark, there's no chance. Still, it's only a small part of the equation.
2. Dedication
The writer must put her money where her mouth is, making the work a priority in terms of time and energy. The world is full of people dedicated enough to attend meetings or classes and talk about writing. When it comes to putting in the sweat equity, however, the field thins considerably.
And the dedication can't stop with the actual writing but must extend to a systematic study of the craft of writing, the business of writing, and competitive books within the targeted market area. If you aren't voraciously reading in your chosen area, you aren't absorbing reader and editorial expectations, and that lack of knowledge will brand you an amateur when you make your submissions.
All the meeting/conference/academic class attendance awards in the world won't serve as a substitute for doing the reading.
3. The Kernel of Arrogance
It takes just a tiny bit of arrogance to believe you have something to say that's worth the world's time, that you're good enough to merit the dream that you're pursuing. Think of fighter pilots, star quarterbacks, and those testosterone-drenched business tycoons you love to hate for their swagger. You're going to need a measure of it, not on the outside, where it will be deemed obnoxious (especially and unfairly if you're a woman!) but in your heart, where it will steel you for the coming battles. A pro must have enough confidence to face down rejection and keep fighting.
4. Tolerance for Risk
Writers' workshops are brimming with those who spend year after year (sometimes running into decades) overpolishing the same darned opening chapter. A pro finishes things and takes the next step, risking critiques from unbiased readers (not ammother or a sister!), entries in contests for blind feedback, and (gasp!) submissions to appropriate editors and/or agents.
After a few rejections, the dilettantes go cry in the corner and find another hobby. The pros just lick their wounds and get back up, blood in their eyes, to continue the fight.
5. Business-like Attitude
Writing is a hobby, publishing a business. Those who move beyond the amateur stage treat it as such by learning about agents, publishing houses, and book contracts. This step held be back for a long time (I wanted to be about art, not filthy lucre!) but two resources that got me over the hump with Richard Curtis's How to Be Your Own Literary Agent (read it, even if you already have or plan to get an agent, so you can intelligently discuss important issues with him/her) and agent Donald Maass's The Career Novelist, which is now available as a free PDF download from Mr. Maass's website.
6. The Stubbornness of a Mule, the Hide of a Rhino, and (Insert Your Own Cliche Involving Persistence)
For the vast majority, the quest for publication is no sprint but a mega-marathon. Chat with any group of traditionally-published novelists, and you'll generally hear stories of those who wrote three, four, even six or more full manuscripts before selling. With each effort, something new was learned.
As Calvin Coolidge reminds us:
"Nothing in this world can take the place of persistence. Talent will not; nothing is more common than unsuccessful people with talent. Genius will not; unrewarded genius is almost a proverb. Education will not; the world is full of educated derelicts. Persistence and determination alone are omnipotent. The slogan 'press on' has solved and always will solve the problems of the human race”
So there, in a nutshell, are a few ways professional writers, and those with the potential to go pro, recognize others who have what it takes. Look at the list and think about areas you may need shoring up.
Then go find yourself some other guns and make some art.