that you're pretty sure is counterfeit. I'm 99% sure this coin is counterfeit, but I love the history it represents.
I wouldn't be so sure that was counterfeit, since I believe the originals were made under pretty primitive wartime conditions, in a pretty chaotic and difficult time and place in history. That being said, I don't know. I would defer to those more experienced in this issue. The rather soft detail does look a bit suspicious, but I'm not sure if any originals look like this. It's possible? I am familiar with this type from reading about them, but have never owned or seen one in hand. Get it checked out and/or third-party graded, if you're so inclined. You might be surprised. (Or not.) What makes you suspect a counterfeit? It is entirely possible you know more than I do.
Most 20 mark tokens are counterfeit. Only 600 genuine tokens were struck, so they are both valuable and rare.
and yes, I have kept counterfeit coins for two reasons, mostly. One, because I don't want someone getting taken, and two because they're interesting and make great teaching tools.