Lock me up and throw away the key

I should probably google this before I post it.... I'm not sure why but on many bridges there are locks decorating the fences. I like this tradition even though I don't get it. It's beautiful.

UPDATE: They are love locks. Lovers chain them there as a symbol of their devotion and throw away the key. Note to self, remember to look down at the water below. I imagine a wishing well of keys.