Depending on your geolocation you may have walked across a bridge recently that seems to have some art installation, or a type of weird encrustation smothering the ironwork.  If you stop and take a closer look, you'll find that the colourful decor has been provided by countless miniature padlocks, often engraved or individually marked somehow, and then permanently attached to the railings.

What on earth are they? And more importantly, what do they signify?

Padlocks of Love

The simple explanation is that the padlock symbolises never-ending love.  The couple choose a lock and add their name.  After they've firmly attached the lock to the bridge of their choice,  they throw the key into the water. The lock is a permanent reminder of their love for each other.

Once upon a time, lovers engraved their initials onto the bark of a tree, often inside the outline of a heart, sometimes with cupid's arrow going through it. Luckily for trees, at least, this tradition is  now less common than using a metal lock to symbolise your passion. Carrying a pocket penknife also used to be an acceptable practice. Knife carrying is now frowned on, so maybe it's less easy to carve a heart onto a tree.