Notice: The 1000-use codes that came with RIFT’s 4-year Anniversary Infographic have now become unlimited-use codes until 14th March 2015.
The codes are now unlimited use, and will instead turn off at 11:59 PM PDT on March 14th.
[Source: CM Morgana]
Here’s the three codes:
J3PN-NXKR-GRKQ-WYHN-2RNK
RMJR-3EKZ-JZKD-LXGE-YQZG
T6NG-NP9N-HPPY-3CYJ-RM7E
They are for a Dwarven Smithy Goggles (helm costume), Hooty companion pet and “the Devotee” title.
You can redeem them by logging into your account on the RIFT website and going to RIFT’s Code Redemption page or the Apply Code page.
Note: If you have previously applied a code to receive any of these items, it will show up in your Apply Code/Redemption page, but you won’t receive that item in your in-game mail. (Thanks to Zaber for the info!)
Troubleshooting: If you are having issues redeeming the codes, try logging onto the RIFT website first before applying the codes. There seems to be a potential issue with trying to redeem the codes if you aren’t logged in when you apply the code.
RiftGrate 
It seem that if you have Dwarven Smithy Goggles and Hooty companion, the code works, but you will not get it again in the mail.
Noticed that when I applied the codes. Trion probably has some code in place so you don’t end up with multiple mails with the same item on every character (though I’ve experienced that with a few mounts).