The Iron of the Bow (in Venetian “fero da próva” or “dolfin”) is the metal part that stands in front of the gondolas. It has a meaning that very few people know about.
It is mistakenly said to have the purpose of protecting the bow from possible collisions and embellishment. In reality, the Iron of the bow has an essential and very precise function: being very heavy, it weighs down the bow of the boat and keeps it always in trim with any number of passengers.
The Iron embodies the essence of Venice. The large “S” Metallica, which makes up almost all of it, symbolises the Grand Canal, whose shape it recalls. The upper part symbolizes the Doge’s hat. A small crescent recalls the silhouette of the high bridge and the plane of the San Marco basin. The six rectangles on the outside symbolize the six districts of Venice, while the inner one recalls the Giudecca. The three metal cuts inside the spaces left by the above mentioned rectangles symbolize the three most important islands of the Venetian lagoon: Murano, Burano and Torcello.
More info: https://it.wikipedia.org/wiki/Gondola