VGFacts

An unnamed programmer "The Hanafuda Captain" hid a message in the NES Classic Edition's code that reads:

• "This is the hanafuda captain speaking. Launching emulation in 3...2...1. Many efforts, tears and countless hours have been put into this jewel. So, please keep this place tidied up and don't break everything! Cheers, the hanafuda captain."
  

"Hanafuda" is a reference to the playing cards Nintendo sold before entering the video game business. 

System hackers also found that the system has slots for 60 games, double the number of games on the system, although the process to upload games on the system is not quick and could permanently disable the system. 

http://www.eurogamer.net/articles/2017-0...ed-via-usb
http://www.eurogamer.net/articles/2017-0...n-nes-mini
http://kotaku.com/hidden-message-found-i...1790967522