This ain't legal advice, just how I understand it.

Trademark ain't the same as copyright. It's generally used to protect a business from impersonation by its competitors. The phrase "WhiteRabbit" could be trademarked by a company, but all that does is prevent other companies from using that name — and they might still be able to if they do an entirely different business.

The phrase "WhiteRabbit" is just two word glued together, so that would be entirely fine to use, but so'm like "Microsoft", which is quite obviously tied to a company, might not be. That's assuming s/WhiteRabbit has no'n to do with the company WhiteRabbit.

I ain't never heard of a company trying to take down a forum because its name is too similar to their trademark; the policy is mostly just in place as a disclaimer. I wouldn't worry about it, and if SaidIt ever got a C&D: they'd try to work so'm out to keep the sub online.