" It is also worth noting that fan fiction and fan art can be a trademark violation as well, especially if it uses names and titles in a way that causes confusion as to whether they are official. Trademark disputes over fan creations are rare, but still possible. If you’re interested in creating fan fiction or fan art, here are a few quick things I would say to do to make sure you don’t find yourself in a copyright or trademark conflict. (...) 2.Make it Clearly Unofficial: Have clear statements on your site that your site and your work is not an official site and is just a fan creation. Though it may not help with an actual trademark or copyright dispute, it shows good faith and encourages rightsholders to work with you. "
Seriously, don't worry about it. You're not selling anything. You're art is helping them, not harming anything. You are a gold mine to a company because you are functioning as a natural marketing tool to promote their art. Some people may get a hard on over it about ethics but who cares. Welcome to the internet. I personally am not going to put other franchise's logos on my art but that's my preference. You're harming nothing. It only becomes an issue if you start selling these prints and trying to pass them off as authentic. So my advice is to keep doing what you're doing and don't worry about it. Telthona is more conservative it may seem but that shouldn't concern you.