Under lock (and key?)

I've seen this tradition before, but I have no clue about the real background... Lots of locks with 2 names on them, so I guess it has something to do with love/relations.

I could find something on wikipedia probably, but backblipping and still have lots to upload using the slooow wifi here so i'm playing lazy :)

edit: found some wifi, so there we are: love padlocks