I wrapped the Bar Code Clock by Scott Blake in OS X Dashboard widget skin.
Download and keep it in your Dashboard if you like it, but it's more a proof of concept than something I would use daily. 6 to 8 %CPU (at 1.5 GHz PowerPC G4) is an overkill for just a silly clock.
The clock uses 12-hour system. Licensed under the Creative Commons Attribution-NonCommercial-ShareAlike license.