Light Poles and Yogurt pots?? Help??

This is going to be strange post today and I am hoping that the Oxford visitors to the blog will be able to help me. Over the last week or so I have noticed on a number of light poles around the city at about 4 metres from the ground an empty yogurt pot taped to the pole. What are these for? Who put them up? And have you seen any? I have seen them on Parks Road, St Giles, and Onsey Lane. I have also seen on different poles a small clear and green vile, but I have only seen two of these so far. Post any sighting to me please.