My wife does things like that. I've finished the basements in our last 2 houses and she likes to put HMs and write love notes to our kids on the insides of the walls, under the flooring, etc. Then we take pictures of them to show the kids when they grow up. Yeah, way goofy, but it makes her happy!
And like you say, it's kind of cool thinking that someday, someone might take up the flooring or cut into a wall and find evidence that she was there.
