This clip shows that Kellerman did not turn around while passing behind the sign.
Are you claiming to be able to see through the sign?
No, Kellerman didn't have time to turn around.
Kellerman was out of sight behind the sign from frames Z204-Z219, less than a second.
The first gif is Z198-Z219, just so you can get a good look at Kellerman.

The next gif is Z204-Z219 and @ Z204 we can see his hairline and the sun shining off his forehead at the same angle.

Now when Kellerman actually does turn around he has to shift his whole body slightly forward and turn his torso so he can see Kennedy. For all the frames before and after the sign Kellerman is simply looking in one direction, he may have looked towards Greer and returned his head to the exact same spot but a full on turn, no way.

But maybe Kellerman didn't need to turn his body around to see behind and was possessed and could just spin his head?

JohnM