On the clock tower of the Palazzo del Podestà on the Piazza Broletto in Mantova there are six Coats of Arms of the sister cities and also one of Mantova itself. They are colored tiles attached to the facade of the tower and separate tiles showing the date that the partnerships started.
In the center we see the coat of arms of Mantova and the one of Charleville to the left and the one of Nevers to the right of it. Under the three is the date "September 1963". Right of the three there's the coat of arms of Puskin and the date "November 1993". Since there was not enough room for further tiles, they continued towards the left with the coat of arms of Weingarten and the date "March 1998", Madison with the date "December 2001" and finally Azuchi with "February 2005".
According to Wikipedia there are partly other years and more sister cities, but it seems as if these additional cities were not added with additional tiles.