Just remembered another difference between trademarks and other kinds of intellectual properties: someone does not need to be the creator of a trademark to register it. He just needs to make sure no one else has registered the same or a similar trademark, or was using a similar trademark unregistered, in the same field or a related one, for some time prior to the trademark request. An unused trademark is ripe for anyone to claim.

I don't know the specific time frames for US law, but in the country I live, if no one has used the trademark without registering it in the previous 6 months, or if the owner of a registered trademark hasn't used it in the previous 5 years, it's open for anyone to claim.

In short, if the rules in the US are similar, in the absence of a previous register or valid contract, what matters is who was using the term, in the same field, prior to the trademark request. If the answer is "no one", or if the answer is "just the guy requesting the trademark", then it will most likely be quite hard to block the trademark request.

(Yeah, this does means anyone can "steal" any unused trademark. It's intentional, in order to clear the field of stagnant trademarks, and make them available for use anew. If someone wants to keep his trademark, he better use it.)