For many longtime Walking Dead fans, the appeal of the hit AMC TV show meant falling behind on the actual comic books from Robert Kirkman and Charlie Adlard. That means there are tons of Day 1 comic readers, who didn't want to potentially spoil the show, that may not know what happens after the Negan arc runs its course. If you don't want to have that spoiled...
TURN BACK NOW.
After a Negan is successfully "dealt with" The Walking Dead comic book introduces a massive time skip with many new, safe settlements springing up. Rick Grimes becomes something of a living legend and Carl struggles to live in his father's shadow. However, that's just the backdrop for the introduction of a new threat. What seemingly looks like Walkers talking or "whispering" turns out to be other survivors who learned to blend in by wearing the skin of other recently deceased survivors. Remember early on in the series when Rick escaped out of the tank in downtown Atlanta by covering himself in horse intestines and blending in with the horde or Walkers. Well, these guys have taken that concept to the next level. Instead of harming the undead, they live among them. Introducing The Whisperers at this stage seems a tad premature as there's still a ton of material with Negan to explore. Most fans expected the Negan conflict to take a full season (if not two) to fully depict. The Instagram tease has led many fans to wonder if the arc will be shortened due to Jeffrey Dean Morgan's limited availability.
As for the Instagram post itself, the image itself is a clue as a major turning point in The Whisperer arc is when a few members from that group take of their Walker skins, infiltrate a settlement and capture a number of residents. They aggressively establish a boundary by cutting of the heads of those captured, placing them on pikes and lining them up to form a borderline. One of the lines The Whisperer leader says to Rick is, "You've been warned."