Let's go over the ways you can create files to make an open source hardware design spread:
- AutoCAD files (and other files usable for 3D printing and related manufacturing, e.g. CNC machines)
- Data sheets
- Materials lists
- Assembly guides
You should apply the license to the AutoCAD files and blueprints.
You don't spread open source hardware by making physical objects available. You spread it by making the design available. Apply the license to the documents/files behind the design.
However, you can, if you want, add the license to the physical object (and sometimes it is required for some objects; see below).
Here's a specific case. From a page about the TAPR Open Hardware License:
If you create a design that you want to license under the OHL, you should:
- Include the OHL document in a file named LICENSE.TXT (or LICENSE.PDF) that is included in the documentation package.
- If the file format allows, include a notice like "Licensed under the TAPR Open Hardware License (www.tapr.org/OHL)" in each documentation file. While not required, you should also include this notice on printed circuit board artwork and the product itself; if space is limited the notice can be shortened or abbreviated.
- Include a copyright notice in each file and on printed circuit board artwork.