M on top of Coagulation

On Coagulation there is a McDonald's Sign that can be viewed in game.

It is disputed whether this is in fact a third Megg Easter egg or not, but this seems to be up to speculation and player interpretation.

Walkthrough
It is most obviously a "megg"   strange obsession....

When you finish this go to blue base in Coagulation. Use the Spectre's boost to climb up the right part of the cliff near the base. There is a ridge on the wall as you continue left that forces you down, so stay clear of it by moving slightly down from it.
 * First, change your character model to an Elite, if it isn't already (this is needed because they get out of the Spectre from the front) and make a gametype where you have:
 * an overshield
 * a couple of Spectres.

By now you are completely sideways, and approaching a ridge on the cliff. keep boosting on it, and you'll eventually get over it. It may take a few tries but just be patient and keep trying.

When you get to the very top of the cliff, turn around in your Spectre, keep its left wing on the rim you originally approached, move the nose of the craft slightly over the rim, and search for a small notch in the cliff. I'm not entirely sure whether it was pure luck or timing that got me over it, but you have to get out of the vehicle and hopefully you will be over the level.

Now to find the sign. Walk along the cliff to red base but DON'T walk on the edge! There are notches in it that you can fall into and never get out of. Once at the back end of red base's cliffs, look around for a white patch in the rock. At first it won't look like anything, but back up and look again. There is an M clearly visible on the cliff. Technically, it isn't really a "sign", but it is an M.