Ideas were all great, but I ended up going with a BOokmark scheme where I bookmarked the signature images with a standard naming system. I then went through all Bookmarks in the document, deleted the selections, performed th email merge, and closed without saving.

The advantage of bookmarks is that they can zero to a location no matter if it is within a text box or within two layers of text boxes. These documents have almost 100 text boxes in them, so wading through the SHapes collection to find my images would have been a little more involved.

Thanks to everyone for the help!

JoeK