Bungie created Halo. Now they have moved on to "shared world" sci-fi shooter Destiny. That does not, however, mean they have left the past behind. It's just, um, on the back of a tower now.
According to Reddit user SmokingGhost, you can find the very... familiar-looking tower during a Mars strike mission. "It is the back side of the building that the first and second lieutenants are in or go to," they explained. "You can see it also when going toward the third one in the tank if you turn around and look up to it like I did."
They also posted a video of their masterful find here.
Here, for reference, are some pictures of Master Chief when he's not being a tower:
It's tough to say if this is an intentional easter egg or not, but signs point to yes. Bungie has a long history of referencing its past in newer games. For instance, the Halo series is littered with story scraps that point to a (never officially confirmed) link between Master Chief's ring-trotting, moonwalking adventures and the less well-known but equally revered Marathon. And hey, Halo 5 -- which is being made by 343 Industries, not Bungie -- is subtitled "Guardians." Hmmmmm.
So there we go. By way of the transitive property, Destiny, Halo, and Marathon are all knit together with the dangling threads of their universes -- a grand tapestry first given life decades ago. Or Destiny just has a big, wonky-looking tower that kinda resembles an armoured dude's face, and everybody's reading way too far into it.