As I understand it, the title of the story is taken from an old Vietnamese folk tale. The folk tale has to do with a fisherman who was out fishing and dropped his sword (don't ask me why he had a sword) in the lake. He wanted to be able to find it again so he made a mark on the side of his boat to show where he had dropped it.
The protagonist of the story does a similar thing, in a sense. He too has something that he loses and would like to find again (the woman). But he, like the fisherman, does not have any good point of reference for how to find her because all the houses on her street look exactly the same and there are no cross streets or anything to tell him where to look.