Love locking is a tradition thought to origionate in China, but apparently its pretty big throughout Asia and Europe. The details vary, but the basic concept is the same. Couples write their names on padlocks, and then fasten them in public places and throw away the keys as a symbol of their unbreakable love (pause for awws).
Love locks can be found on fences, lamp posts, fountains, benches, and just about anything else you can think of. Pécs in Hungary have had to introduce special 'love walls' to stop the streets becoming unuseable!
Mostly, the couples toss the keys into bodies of water, but some areas provide special bins! In some countries, love locks are placed by newlyweds on the day of their marriage, to keep their love secure. In other areas, the padlocks are set in place by couples in love but not yet married to bring luck to their relationship (Fu. Thats good luck in Chinese, I learned this today). The fountain below is in Montevideo in Uraguay, where there's a plaque encouraging couples to place a lock. It promises that if they then return to the fountain, their love will last a lifetime.
Probably very annoying for local councils, but undeniably cute. I wonder if you could do them for friends and family aswell as lovers? Pets? Ice cream?! Ice cream is my soulmate.