You will see what the W's are for I believe in the finale.
I was thinking the whole season they'd introduce the Negan character but I don't believe that will happen yet. With the way this is going what I think is going to happen is this.
The town is going to consider removing Rick. While he's in trouble Jesse will kick Pete out of their house and you won't see him all episode. At some point they're going to be gathered for something, possibly the discussion of removing Rick from the community and Pete is going to show up to try and kill Rick (Who they haven't yet kicked out). Deanna, or her Husband, is going to try and stop this from happening, cause they don't want the violence or whatever, and Pete is going to wind up killing whichever one it is. Right now I'm thinking her Husband. which will finally cause Deanna to give Rick the authority to take Pete out.
Also at this time this is when they're going to be attacked by a raiding group. I believe they're going to be referred to as The Wolves, which has been a rumor all season long, and they're basically going to be the people who replace the bandits known as the DC Scavengers. These will be the people that will explain your W's on the heads of their victim's. I do believe that they're funneling the zombies to the area because they want them to be a distraction so they can raid the community as well. As you could tell from the episode they obviously use live bait to lure in Zombies (The woman tied to the tree and eaten alive).
They will make their attack on Alexandria and attempt to take it over and take what's there. The people, led by Rick, will stop this from happening and this will lead to Rick becoming the leader of what will become known as the Alexandria Safe Zone. They might end the episode with the attack and next season you'll find that they held them off and Rick is now the leader, proving he needed to be in that place after all this.
I'm thinking the episode will actually end after they hold off the attack, which is why they extended the episode to 90 minutes so that you can see them fend them off and it will end with people wondering if Rick will not be the defacto leader, which you'll learn at the start of next season that he in fact was made the leader because of all this.