W3C or World Wide Web Consortium, launched the official HTML5 Logo today.
You can head over to the official site and choose from a variety of logos according to the features & services you are using in your web applications and start embedding them in your websites.

According to W3C:
It stands strong and true, resilient and universal as the markup you write. It shines as bright and as bold as the forward-thinking, dedicated web developers you are. It’s the standard’s standard, a pennant for progress. And it certainly doesn’t use tables for layout.
We present an HTML5 logo.