I am sure you've heard of the tradition of placing locks on bridges and then throwing away the key. I believe it started in Paris though the bridge there had to remove the locks because of the weight and what that was doing to the bridge fencing.
In our travels along the Rhine we saw some of these locks.
In Cologne our tour guide took us across a bridge and we returned on the other side. One side had fewer locks then the other. The tour guide said he'd put a lock on there too.
In Basel the bridge railing did not lend itself to attaching a lock but the door to this monument on the bridge did.
Have you attached a lock somewhere?
[We saw locks attached to a bridge in Harper's Ferry, WV too.
See that here scroll down to the last photo.]