Perhaps this custom is practiced somewhere nearer home, but I first saw it on my recent trip to Spain. Mike and Noza sealed their love with these locks left "forever" on a bridge over the Ebro River in Zaragoza. The entire railing was dotted with these very visible tributes to various relationships.
The practice wasn't particular to one bridge. These padlocks hung on a span over the Rio Onyar in Girona.
The Catalan flag in the background was most everywhere in that city.