To be a professional SEO member, you need to hang out within the SEO community and circles. There are several SEO sites available online
Join them and participate in conversations. The goal is to learn and obviously, give something back to the community.
You can also create social media profiles (twitter, LinkedIn) and join groups related to SEO. Again, participate in conversations and ask questions/provide answers to newcomers if you have the knowledge.
There is no such thing as an SEO Body/Authority as SEO is always changing in tune with the Search Engines algorithms. Do not fall into the trap of buying paid listings from the so-called “SEO Independent Authority sites” that can measure your performance.
Show that you are knowledgeable, learn and teach, ultimately you will reap what you sow and hopefully be a trusted source for SEO information and will be recognized in SEO circles.
Obviously, apply what you’ve learnt and taught onto your own projects and show your results to the community. Anything except white hat SEO is not welcome, so tread carefully! Check the Google SEO Guidelines for more information.