As @cybereality has already correctly pointed out, in most countries that respect intellectual property you do have the copyright automatically if you created it, I believe the legal term is called 'creative license' however, obligatory I'm not a lawyer on all of this I do know a bit though. Really you should only worry about trademarking and copyright as an indie if you start making a significant amount of money. In my country at least, you can also apply for a trademark on whatever you've made with a fee and then you'll officially be registered.
Really though, I think that the best thing you can do for yourself is constantly make records of your progress, this is why uploading WIP footage of your projects is always a good idea. Even if some douche does manage to trademark your IP at the end of the day, your long term followers will see exactly what you've been up to and even someone new will be able to recognise the fakes by glancing through your social media.
This is also what can hugely separate us from the big companies, a lot of indie devs have no problem showing their whole process and a code snippets which creates a lot of transparency and shows gamers we're legit, these days I'm instantly suspicious of any game dev that doesn't do that. They're either relying on marketing hype or they're doing a third party asset flip and will disappear when they're found out.