Setting: Though it doesn't have much to do with the topic itself, the setting is the US, modern day.
At one point my character is having an item appraised, and the antique dealer notices a hidden drawer filled with some sort of document. Whatever it is, he tells my main character that if there are more of them, they could be worth a lot of money.
This was a dream, so I'm not really sure if there is anything that would fit that description. But if anyone can help, I'm looking for some sort of old financial documents that would be used around the late 1800s in the United States. It has to be something that wouldn't be worth a whole lot on its own, but would suggest that there was something of value elsewhere. I don't know how that stuff works, really. Financial documents from the days before computers, I mean. Anyone have an idea?
Searches: I have no idea how to even search this sort of topic, so search ideas are helpful, too.
Edit: Just for clarification, the thing she finds doesn't have to be a document, but it has to make her want to search through an old attic. The antique is from her grandparents house, so she figures that would be the place to look. I thought a document would work best, since she would feel compelled to look through all of the old papers. But anything that would get her digging around in the attic might work. It just has to be something you could hide in a box or something like that.
ETA: I think I've found what I need! Thank you all for some great suggestions!