Update: Twitter just posted an official announcement about this, with a link to a sign-up form. The company says:

Soon, small businesses based in the United States will have the chance to take their Twitter marketing efforts to a new level. Starting in late March, we will introduce a new advertising offering that makes it simple for companies of any size to grow their businesses using our Promoted Tweets and Promoted Accounts products.

Starting today, American Express Cardmembers and merchants can register to participate in the initial introduction of this new offering via ads.twitter.com/amex. We will launch this new offering more widely later this year.

Original Article: Back in December, Twitter Chief Revenue Officer Adam Bain revealed that the company had begun testing self-serve ads with some of its existing advertisers.

Now, according to a report from AdAge, these ads have been opened up to 10,000 small businesses – American Express cardmembers and merchants can register to use the platform on a first come, first serve basis. Those who get in will get $100 in ad credits for promoted tweets and promoted accounts.

The offering comes as Twitter has completed the roll-out of its latest redesign. The new design comes with the ability to embed tweet and some new keyboard shortcuts, as well as redesigned brand pages:

“Communicating with users isn’t just about what you say. It’s also about how you say it,” said Twitter’s ad team. “Now, your profile page does more to help you make an impression with a large header image for displaying your logo, tagline, and any other visuals.”

Twitter is cranking up the brand usefulness, and should be cranking up the monetization of the service along with that. Don’t expect the company to go public anytime soon though.