The first puzzle was VERY simple, so simple that many were overthinking it.
A= 6 letters after A = ABCDEFG
C= 2 letters after C = CDE
N= 1 letter after N = NO
Continuing with the next 3 plates until you have the code to type into the page linked in the email, where the mission was revealed. The answer had to be entered completely in lower case, I think that may have been more confusing than the actual puzzle. :-)
On the 3rd plate, for W6 - you go back to the start of the alphabet. So it was WXYZABC
If you completed the mission, finding a cache with more than 10 favorite points that week-end, you received this souvenir:
For us, this meant traveling a bit, since we've found all the caches less than 40 minutes from our home. We found a cache that fit the requirements, and it was a nice large ammo can in a driveway. That inspired this post - There are Better Caches Than an Ammo Can In A Driveway - http://fieldsofhether.blogspot.com/2016/07/there-are-better-caches-than-ammo-can.html