Not in particular - I only know that there has to be an Application that is responsible for displaying the filetype. I would guess that the Application needs an OLE interface as well. There was some paint program that was useful as a target, but I don't recall the name off hand. Also it looks like transparency may not be available using OLE - http://support.microsoft.com/kb/123151 I don't know enough about WMF or DiB to know if they support it, but I'm pretty sure the default BMP does not.
That's why I was leaning towards using Adobe as a place to add the stamp. They seem to handle graphics better than anyone. Though not enough to entice me to sign up for their subscription-only professional Creative Suite. There are other PDF integrators, but I haven't needed to look at them for a while.
Also, it looks like the original poster changed his basis for an acceptable answer, and is going with a drawing symbol. Not unheard of and it works, so that's good.
