A. Mann Daggers are very distinct in their construction. I have located photos of an original.

As I recall the grip should be ivory (not bone). Ted can correct me if I am wrong.
Anyway, look at these photos and see if you have an original.

Polish (110).JPG (38.18 KB, 96 downloads)
Polish (111).JPG (38.59 KB, 95 downloads)
Polish (112).JPG (39.56 KB, 95 downloads)
Polish (113).JPG (39.14 KB, 97 downloads)