If so, wouldnt the implications be legal binding to a person... but also, detrimental to any forum?
https://www.copyright.gov/help/faq/faq-protect.html
You may be thinking of trademark. If your online handle is a trademark, you can exclude others from using it in trade. Linus Torvalds owns the trademark to "Linux" but has licensed it perpetually for free:
Can you trademark a handle? Maybe. I’ve never heard of it happening though.
Copyright? Probably not.