I clocked that a few months ago and did wonder why they'd done that to all the signage that's adjacent to the blue fence.
The blue fence went up when the O2 became an Olympic venue - the mesh is such that you cannot put your fingers into it should you want to climb it.
Conversely, were you to shin up the adjacent sign post, you'd be able to get over the blue fence with relative ease - hence the sign post has the fenced-in treatment.