There's not a whole lot to say about this. It's a biohazard symbol in OpenSCAD, to the exact government specifications. I used this as a reference:
It's done in the 2d subsystem, so you can use it in 2d or apply a simple linear_extrude() to convert it to 3d.
The example STL and DXF files are 51mm across, which is the diameter you get when you use A=1 according to the spec; the OpenSCAD file allows you to easily specify the diameter you desire, and can optionally join the 'inner circle' to make this a single object for printing instead of being 4 shapes as it actually is properly.
Do what you like!
Thanks to my fantastic and brilliant bride-to-be for checking the math.