Halo: Reach’s “I’m Sorry, Dave” achievement is potentially one of the easiest trophies to get in all of gaming. I get the feeling most people searching for this are wondering how they did it, rather than trying to learn how to do it.
You can get the “I’m Sorry, Dave” achievement if you discover the hidden binary signature, and there is a good chance you did this entirely by accident.
To find the hidden binary signature, all you need to do is zoom in with any weapon that doesn’t have a scope, such as Assault Rifle, the game will perform a standard zoom. If you pay close attention to the bottom left-hand corner of the screen, you will see a long string of binary code.
The code will read as 0100010001100001011101100110010, which, when translated to English, spells the word “Dave.” The code is a reference to David Candland, the UX design who spent time working on the Halo and Destiny games, and who now works for Monolith.
To complete the achievement, all you need to do is zoom with an unscoped weapon and hold the zoom for a couple of seconds. That’s it. A straightforward achievement to get. It is almost certainly something that you have already completed without realizing how you did it.