Hi M.L.,
what do M. and L. stand for?

As far as I understand your question, you would like to
insert a signature at a certain place in a doc, and have
appear it on other places, after updating fields.
I have to admit, I hate coding with fields. IMHO there is
too often no logical way leading to a solution.
And I am therefore no good at it.
What I would try goes like this:
Manually, e.g. in a template:
Set a bookmark "signature"
set references to that bookmark, wherever you like.
{ REF signature }
Programmatically:
Add a field at the bookmark "signature",
which causes the bookmark to disappear.
Set the bookmark again to the range of the field.
Update all fields.
---
Dim f As Field
With ActiveDocument
Set f = .Fields.Add( _
Range:=.Bookmarks("signature").Range, _
Type:=wdFieldEmpty, _
Text:="INCLUDEPICTURE ""c:\\test\\test.bmp"" ", _
PreserveFormatting:=True)
f.Select
Selection.Bookmarks.Add "Signature"
.Fields.Update
End With