When you go to halowaypoint.com and check your personal terminal records, if you do certain accolades you unlock certain terminals but you also have to use an access key which is always a pattern of forerunner symbols.
This is one of those, "hidden" in the news splash of the website, as a really simple horizontal puzzle, which I solved for you.
Complete the required challenge, input the code, receive candy.
One of these days they'll institute a mandatory skill and intelligence test for WoW. Only one server will be necessary after that, and it will be glorious.