Any question answered...

The marking is what is known as a 'jug handle' (because of its shape) and its purpose is to introduce shared-use provision (walking and cycling) on the footway there to enable cyclists to ride up to the 'Toucan' ('two can' cross, i.e. people walking and cycling) crossing, which they obviously wouldn't be able to access unless they were on the shared-use 'footway' first. If you look at the whole junction, all of the crossings have the dual provision of the normal pedestrian lights and the additional cycle green light. This means that all the footways around have to be shared use, and you can indeed see more 'jug handles' and the blue 'shared use' diagram up on the lamppost on the footway around that left turn.

In one of the many little absurdities usually thrown up by these crap designs, there's no 'jug handle' where the dropped kerb is for the residential driveway entrance, probably because the distance between the corner and the driveway entrance is too short for one and it seemed unnecessary to the engineer. By the logic of the design, there should really be one, both for clarity and because there doesn't seem to be any indication of where shared use really ends. I can't see any indication that shared use continues along the A205 London Road, but you could perhaps argue that the signing and marking is misleading if you were stopped for riding along the footway.

But yes, the signs indicate that shared use is lawful along this piece of footway around the junction and you're quite within your rights to mount the footway and turn left in this way. You should obviously take extra care in re-entering the carriageway at the driveway, because chances are that when you turned the corner the main drag will have had a green light, or that Sydenham Hill will have had a green light in the meantime, while you have to look up to 180 degrees behind to see what's going on. Both factors increase the possibility that you may come into conflict with traffic on the A205 after turning left at red in this way.

You and that swiss guy would loose your shit completely here in Berlin