I recommend to just apply the well-known free licenses to your project and not using any logo of any political organization, including the "OSHW" logo.
Your open hardware doesn't require approval of any political organization. We are free to develop what we want without anybody awarding us a "certificate". Likewise, we can develop free software without the official approval of the FSF.
The OSHWA state their purposes are to "organize conferences", "educate the public", and "organize the open hardware movement around shared values and principles". They say:
So why do you need a license at all? Is it enough to just add a disclaimer that your project is “open” and distribute it for the world to use freely? Unfortunately, probably not. Without a proper license or certification, it’s too risky for downstream users to implement or add to your invention without fear of legal liability for infringing the intellectual property protections that may cover your project. Licensing and certification solve this problem. By attaching the appropriate licenses to each applicable element of your project, you empower downstream users to use, recreate, modify and distribute your designs without needing additional permissions and without fear of legal repercussions.
Yes, your project must be licensed under a free license in order to be freely usable by others. However, it doesn't need legal certification. This is a ploy. They go on:
After completing this guide, you will have the knowledge to self-certify your product as OSHWA-compliant open source hardware. This allows users to know that your hardware complies with the community definition of open source hardware.
So, you "self-certify your product as OSHWA-compliant", and
"OSHWA compliance" is equated with "the community definition of open source hardware".
However, the OSHWA doesn't have the authority to speak for the community. It doesn't represent the community at large, it doesn't have any mandate for that. They just want you to believe that they do so that you spread their influence.