Is advertising a sale on the anonymous auction house bannable in anyways? I have something to sell for quite possibly a few hundred million gold but at the same time not many people may be looking for this item in the first place. I want to put it up for bid in the AH but also want to advertise that I have done so in various forums or so forth to let as many people know about it as possible. Is this action against the Anonymous sale policy and bannable as a result?
As Blizzard take a cut of your final sell price, they won't have an issue with you advertising the item both in game and outside of the game. In fact - they even provide a trading forum on the official Diablo 3 forums (EU, US) and a trade channel within the game itself.
The only thing that I could see you doing while advertising that might cause issues is if you ultimately end up spamming trade too frequently to get yourself seen, or bumping your forum post on the official forums too frequently. Blizzard's general rule on this is not to bump any thread of this nature until it falls off the first page.
Any actions that you take on third party forums are not bound by Blizzard's rules.