How to cite marginalia in a second-hand book? So this is an interesting thing I've come across.  I recently purchased a modern book for my research and whoever had the book before me had some pretty great things written in the margins.  

As a medievalist, citing marginalia is par the course, but this strikes me as a bit different for two reasons:


Normally, we cite the library where the book came in our works cited so that others can reference it.  In this case, it's in my personal library.
I don't know who actually wrote the marginalia, but the likelihood that they could be actively publishing now makes me less inclined to want to "steal" (scare quotes because obviously I'm intending to cite it) their ideas before they get a chance to, something that's definitely not the case with books written several hundred years ago.


What approach should I use to using the marginalia both in terms of integrating its ideas into my work (as if it were another paper, though obviously not peer-reviewed) and in terms of citing it (I'm using MLA 7, but may need to switch to MLA 8 depending on when I finish this particular work)?
As far as I can see, you have 3 options: not using the material, using it without citing it and using it with citation. As you have no idea whether anyone is ever going to publish the ideas in those margins, not publishing seems overly cautious. Especially since you want to use the ideas there but seem to have no other source to credit.
Using without citing it seems like a very bad idea. Even disregarding the risk of the original author of those margins coming forward, passing someone else's ideas as your own is unethical.
That leaves citing the margins as is. You could explain the unusual circumstances in the publication you intent to use it in. If you have a personal webpage, you could publish photo's of the margins and also refer to those. Also you could simply offer anyone interested in those margins to contact you.