This is a fascinating mystery. Far from San Marco, on a building in a quiet residential section of Giudecca, is this relief which shows an image of the Ponte della Paglia shrine, Madonna of the Gondoliers, along with the prow of a gondola. As far as I know, it's the only case where a Venetian shrine is honored in a reproduction like this.
I wonder if this is or was the home of a devout gondolier. Another theory (thanks Bert!) is that this relief used to be inside a shrine but is now on its own. In "The World of Venice," Jan Morris mentions a votive shrine that was erected on Giudecca by gondoliers to thank Our Lady for not letting the new-fangled vaporetto drive them out of business.
You can find this relief at Dorsoduro/Giudecca 383, Fondamenta de la Palada.