That sounds confusing. Hodgman, if a trademark is not registered does it carry the same weight legally?
In simple terms, it can, yes (but not always).
And, if I understand it correct, one could choose a game name that appears to be original but find out later it's trademarked by someone but not registered?
Yep. You could also choose a game name that appears to be original but find out later that it is registered by someone but you missed it somehow. Or maybe it's registered in Italy but not the US :P
In any case, trademarks aren't automatically enforced by the trademark police -- it's up to the trademark owner to enforce their rights themselves by hiring a lawyer and threatening to sue you.
Pretty much anything can cause someone to call their lawyer and threaten to sue you though...
On the bright side, usually people start with threats -- they'll usually send you a "Cease and desist" letter, saying "Stop doing this thing, or I will sue you", which gives you a chance to avoid trouble if you don't want to fight over whatever the issue is.
If you're in business proper, you should talk to a lawyer about pretty much every business activity to find out how to best protect yourself legally.
If you're more of a hobbyist, then just use common sense to try to avoid trouble. Do your best to avoid infringing on existing trademarks and cooperate with any businesses that do contact you.
BTW, trademarks are only valid if they're being used to trade a product in the same market as you. If you can't find any evidence of a product being bought and sold under a particular name, then there's a good chance that this name is safe for you to use.
Also, if you haven't actually released your game yet, then technically you can't be using a trademark as you're not trading any products :wink:
I'm not an expert or lawyer, but I believe in case of dispute the one who proves they used that title earlier will be assumed to have ownership. Therefore, automatically you cannot use any existing titles. Sometimes even similar ones.
There's also cases where a newer brand has won a case against an older brand :(
At it's heart, it's supposed to be a consumer protection law that allows people to avoid counterfeit products. A dispute will involve both sides trying to prove that the general public associates their brand with the trademark more than the other brand.