Here is the logo I use for my hardware (electronic) project to show it is open source:
Why I created it is well explained in episode #013.
You can customize and download the logo using the open source hardware logo generator. How it works is pretty well described in the source files.
The generator allows to export in the following formats:
You can download the files thanks to FileSaver.js. And you can get all formats in a .zip file thanks to JSZip.
a brief history about the OSHA and MY open source hardware logo: