It's difficult to say for sure whether you are "in commerce" but we think there's a good possibility that you are, regardless of whether you make money. You are likely offering "services" whether or not you accept compensation or charge for them. Making money probably has more to do with the issue of damages. A lot of trademark owners don't bother chasing uses like yours because if they win, there are no profits to recover in damages. (Selling ads would of course generate income that might be recoverable.)
Are you headed for a lawsuit? That depends on whether the owner is puffing or really intends to do something about your use. In your favor: you're obviously in a different
trademark class (although you may overlap if your forum caters to education and fashion); and the other party's
state trademark registration does not offer as much legal ammunition as compared to a federal registration. (That's because some state registration agencies don't examine applications, they just basically rubber stamp the application without much checking.)
Should you federally register your mark? When you ask about whether you should register your trademark, we assume you're referring to federal registration. If you're considering that solely to block or defend against this trademark owner, it might be too early to take that action; many trademark owners only threaten a lawsuit, and it's possible that this will all blow over. But if you're considering registration for long term purposes -- as an investment in your activity -- then yes, definitely pursue it. (We explain some of the basics,
here.) As for your trademark class, we can't tell for sure but it's most likely in one of
these: 35, 38 or 42. (BTW, trademark mavens have convincing arguments that
'trademark' is not a verb.)
