No, it's not Welsh, or some obscure, long-dead language. Or Martian. It's actually German!
Well, sort of...it's the DFB's (Deutscher Fußball Bund, Germany's governing body for soccer) World Cup 2018 motto for Die Mannschaft's title defense in Russia, and it's all about the power of Fußball to bring people together. "ZSMMN" is the word zusammen (together) with the vowels removed, symbolizing people "scooting together," on the edge of their seats, as they cheer on Team Germany, as well the overall spirit of togetherness and having a common goal among fans of Die Mannschaft.
When World Cup 2018 begins, you'll be able to participate in the #zsmmn hashtag campaign on the DFB Facebook page, Twitter or Instagram with photos and other experiences, as well as follow along on social media and at https://www.zsmmn-dfb.de/en/
Auf geht's Deutschland!!