Three codes were hidden in the SAVE THE DATE: RPE IN CHICAGO post on the Investigate Ingress blog.
[1] op2bc6re7n59pm
[2] cwdicocbcecpdbdadgdecncpdgcacdcecudl
[3] 2104B0413zh1916Ah2116k21182103gB13A2518
Code #1
Observations
14 characters with the right amount of numbers for a valid passcode
Code #2
Observations
Bit of weird one, not sure I have the right solve but this is how I got it
Code #3
Observations
Upper and lower case letters and numbers, big hint to the cipher