This bizarre custom apparently started in Rome, after bestselling author Federico Moccia had the protagonists of his 2006 novel Ho Voglia di Te (I Want You) do this as a symbol of their love on the ancient Roman Milvian bridge. Roman teenagers took up the habit and tourists joined in. Paris had one on the historic Pont des Arts but it was famously removed last summer.
It looks like Birmingham doesn't want to be left out and has also started one of it's own. I'm sure you'll guess what this is all about and what you have to find once you're at the location. All you have to do now is find the right one!
Good luck! and try to be a bit stealthy on this one (tricky I know!)