The borders between Germany and France will see increased security checks
As seen on Facebook:
HEAD'S UP: The borders between Germany and France will see increased security checks in conjunction with the 2016 European soccer championship that begins June 10. Due to the present security situation in France and an expected strong influx of soccer fans from all over Europe, German Federal Police will increase their border policing as part of required additional security measures. Starting this weekend, German Federal Police and their French counterparts will establish various check points at German-French border crossings (including trains) to screen for suspicious persons traveling into France.
The German Federal Police has reemphasized that U.S. military affiliated personnel should carry their passports with them when crossing borders into France to be able to identify themselves with a valid travel document when stopped at one of these check points to prevent holdups and save time/efforts for both the traveling parties and border policing personnel.