A number of international cities with large urban bus fleets have formed an alliance on hydrogen buses. These cities represent leading adopters of new bus technologies on their respective continents and plan to act as leaders in the move to cleaner fuels for urban public transit.
Name of logo and further info here: http://www.bigdeepblue.com/logo_brief.htm
This logo wil be used on a variety of mediums, including print/web, and possibly the side of some buses. So needs to be strong, distinctive, clean & flexible.