Drivers passing through San Francisco have a new roadside distraction to consider: billboards calling out businesses that don't cough up for the open source code that they use.

The signs are the work of the Open Source Pledge – a group that launched earlier this month. It asks businesses that make use of open source code to pledge $2,000 per developer to support projects that develop the code. So far, 25 companies have signed up – but project co-founder Chad Whitacre wants bigger firms to pay their dues, too.