Ever dreamed of being a secret agent or detective?  Here's your chance.  Make it a mysterious date or family night, and see who has the skills to decipher cryptic code.   Simply write each other a secret note in the code of your choice.   You could even pick more than one.   Then trade notes, and see how long it takes you to crack the case and read the message just for you.   You could even finish off the evening creating a treasure hunt for one another or  watching your favorite detective show.

Codes can be comprised of nearly anything , but the most common use numbers, letters, symbols, shapes or even clocks.   A quick google search will bring you thousands of ideas to get you stated.   Remember that to truly be a secret code you'll likely have to invent your own.