There is a sweet tradition in Russia. On their Wedding Day, the bride and groom attach a padlock, engraved with their names and wedding date, to a bridge or "the Padlock Tree" and then throw the keys into the nearest river or lake. The representation is; just as the padlock is locked and bonded with the bridge froever, so are the bonds of their marriage.
In the Town of Riga, there is even a bridge called, "Padlocks Bridge".
Photo from PlayRiga.com
No one knows where this tradition originates or how long it has been around, but judging by the age of some of the padlocks, it has been a long time.