But it's two days later. I'm sorry.

In formal terms, you retain ownership (copyright) of your posts, and grant the HabitableZone a permanent license to display it.

This means that the Zone and I aren't legally liable if you write something that somebody objects to (I'm a "common carrier" in legal terms), and so I have little right to tell you what you can and can't write.

It was the word "allowed" that inspired me to make that clear. I don't exercise that kind of control over the Zone and don't want to (except as forced to by law and force majeur).

Now, as for my advice...

Trademarks and copyrights are somebody's property. It used to be a strict rule that if you used somebody's trademark, like Coke®, you'd have to include the registered-trademark symbol and in a footnote say "Coke® is a registered trademark of the Coca-Cola Bottling Company of Atlanta Georgia".

Things seemed to have loosed up considerably, probably because there's been such an explosion of everybody writing on the Internet that it's impossible to enforce. Though the rules seem just as strict as always in a commerical setting: Pepsi's ads observe all the legal niceties when they mention Coke.

Another nuance is that fiction has always been given a pass in the interests of realism. People in real life conversation don't mutter the trademark disclaimer every time they say the word "Coke", and I'm not sure how you'd even pronounce "®", and so I'm of the opinion that your fictional characters can simply use trademarks in a natural way in dialog. If you want to be extra careful, and a publisher might insist on it, you could put those notices somewhere in the fine print in the front matter.

The flip side of the coin is the upshot of everybody else's advice: Don't engage in "trademark disparagement", even fictionally. As somebody said, it's not safe to write about a real product killing somebody. And be careful that the name of any killer products are completely fictionalized, and not just a couple of transposed letters (that tractor that killed your protagonist's Pa probably shouldn't be described as a "Paterkiller" lest you piss off Caterpillar).

Bottom line: Just use trademarks in fiction naturally, and change the names when necessary to protect your innocence.