They show load on specific 1/3 of the tyre width. As you can on right side,the camber results on higher load on inside than outside,while your left front has pretty low pressure,that's why both sides have more load than middle. Or the wheel stands on some bump of track surface.
PS. No,they are always there,you just haven't noticed them before.
They have always been there, even before the universe began to exist.
As Rony mentioned, it tells how much load is put on each section of the tyre (notice how these blocks change as you take the corner).
Very nice for working out your ideal camber/pressure for a particular corner - you can see exactly when you have dialled in nice, even load across the whole tyre.
Wot! I have never noticed this myself ever or knew it existed myself too. Now my brain registered it and wont be hidden anymore I guess its one of those times for eg. if u are searching your glasses for long time only to find out you are wearing them the whole time.