Trademarks For Open Source Projects?

AilleCat asks: "Recently, the Listar Project was asked to stop using the name 'Listar' because of a trademark conflict with a similar commercial product, ListSTAR, which is understandable, however we've come up with a new name, not to be announced quite yet, until we find out how to protect ourselves from a similar thing happening. Seems in order to hold a trademark, the product needs to be used in commerce. Since we are a small non-commercial free software project (core team of 5 members, and a few other developers), we cannot get a trademark. Someone suggested selling burned copies of the software, but I'm wondering if there are any low-cost ways of protecting ourselves from someone naming a commercial product something similar to our new name, that does a similar thing (like in the case of Listar and ListSTAR) and taking it from us. I wonder how many other Open Source projects are in danger of this happening as well."