The World-Wide Web Consortium (W3C) has unveiled a new logo for HTML5. W3C has introduced this logo and asked the early adopters of HTML5 to put a badge on there sites to tell the world that they are using the latest technology of the open web. Here is the Official HTML5 Logo website. The logo is licensed under Creative Commons Attribution 3.0 — all are free to use and reimagine as they see fit.
The official website also has a badge builder which generates HTML and CSS for the HTML5 Logo that can be put on your website. If you are using HTML5 then use a badge to let your visitors know that what web technology you are using.