I got an email to log in and claim my $5 amazon card. No codes, just clicked on my rewards in the upper left after logging in and it was on both mine and my wife's although she did not get an email. I guess it could be YMMV though.
I appears to be tied to if you did the coke/amazon gift card earlier where it needed coke 20oz bottle caps.
edit: that doesn't appear to be the case according to several posts below.