Mystery Tunnel

So for the last few days the tunnel underneath Rodney Street has seen some rather strange additions.

As well as the ones shown here propped against a cabinet, there are many more strange symbols adorning the sides of the tunnel. They are made out of white gravel and beside each one, err, a pair of white womens' underwear. I took a picture.

Everything seems to be falling apart a bit now, and has either been trodden and cycled over, or blown away. Perhaps it all made more sense when it first appeared.

I doubt it.

Anyone know what it is? I genuinely have no idea. I'm guessing either :

a) Aliens
b) The end of the world
c) Banksy
d) Just some students.