Warning: SPOILERS for The Walking Dead season 7 finale ahead
The Walking Dead has come to another dramatic close in the season 7 finale, "The First Day of the Rest of Your Life," which saw Rick's group team up with their newly acquired allies, the Scavengers (affectionately dubbed the "Garbage Pail Kids" by fans), in order to take down Negan and the Saviors... or so they thought. In a sudden but inevitable betrayal, it was revealed that the Scavengers had sabotaged the Alexandrians' carefully-laid ambush of explosives, and leader Jadis turned her gun on Rick, once again putting Negan back on top in the food chain.
It wasn't long before the tables turned again, however, as Sasha had secretly turned herself into an undead booby trap, by committing suicide inside a casket that Negan had brought along for dramatic effect. The resulting confusion allowed the Alexandrians to fight back against the Saviors, but it wasn't long until Negan had Rick on his knees again. At this point, Jadis revealed the nature of the deal that she had struck: twelve fighters from the Saviors would join her group (later haggled down to ten fighters by way of a staring competition).
Once the smoke cleared and both the Saviors and the Scavengers had been scared off - thanks to some timely intervention by the Hilltop and Kingdom communities - Daryl discovered a small wooden figurine by the gate with two words carved into it: DIDN'T KNOW. This left a few fans perplexed and wondering who had left the message behind. In fact, this is undoubtedly a message from Negan's lieutenant, Dwight, whose hobby of carving the figurines had been established earlier in the show, and who turned traitor against his boss at the beginning of the episode and helped to set up the doomed ambush.
As for the message itself, "Didn't know" is Dwight's way of assuring Daryl that he wasn't aware of the Scavengers' deal with Negan and their planned betrayal of Rick. While it's possible that Dwight is setting things up for his own betrayal of the Alexandrians, he has little reason to be loyal to Negan now and plenty of reason to hate him, so it's fairly safe to assume that he's sincere in his promise to help take down the Saviors.
While Dwight ultimately proved to be of little use to the Alexandrians in the firefight, he will no doubt be a valuable ally in the "All Out War" that's on the way in season 8. Having an inside man so closely placed to Negan could be an ideal way for Rick and co. to learn about the ins and outs of the Saviors' plans, and Dwight may even be the lynchpin that ultimately leads to Negan's downfall. That is, if he can manage not to get killed first.
TThe Walking Dead will return for season 8 in Fall 2017.