From the 8th to the 13th of October, it will be possible to see the blue plastic snails (about knee-high, it seems) placed around on the top of the Duomo. After that date, these pieces of contemporary art will be sold in order to fund, at least partially, urgent restoration work on the Duomo's characteristic and much beloved Madonna sculpture on the tallest spire.
Want more info? Here's the official page on the Duomo's site...in English! (Yeah!)