You want just lines (presumably outside the image) that show people where to fold?
I don't think there's some kind of "publishing marks" feature that will give you fold marks... There are cropping and registration marks available in the Photoshop Print Settings dialog, but I don't recall fold marks.
So you could just go with a simple approach... Expand the canvas (Image - Canvas Size) with a white background, and draw some marks where you want it folded. You could set some guides (View - New Guide) to the precise positions you want first (e.g., 33.3%, 66.7%), then snap the lines you draw to the guides.
Thanks Nick, that is what I thought and was hoping for a script or something for a starting point.