Umm, keeping the fridge clean shows love for each other? I can think of better ways, but they get an A for creativity, and actually there's a couple of decent household tips here.
As for the fridge. I mostly put food in, take it out, eat it. If it crawls out on its own after a few months, I throw it away.
But if you're looking for an unusual way to say "I love you," clean out your fridge--I guess.
