WMF Backstamps / Blade Marks
Please feel free to link to this page.  I've taken these images, myself, so I have the right to release them to the public domain, which I hereby do (i.e., I give up my copyright to them).  I do so mainly because I realize you may not have a camera with a macro lens so cannot get a good image of a backstamp yourself.  All I ask is that you use the right one for the situation.  If the backstamp on your piece has been worn down, either by use or by excessive buffing, please do not represent that your piece has a crisp, clear backstamp.
-  Introduction    Condition Issues 
WMF old triangular backstamp.
The "old, triangular" backstamp or "old mark."
WMF trademarked Cromargan stainless steel in 1927.  This mark is the earliest Cromargan stamp, and it was used from 1928 to 1965.
 
Someone who was selling some MEISTERSINGER dessert forks on eBay told me the backstamp on them is the "WMF in a box" followed by CROMARGAN and GERMANY on the same line, not one above the other.  It seems possible to me, or at least a logical progression, that these backstamps are intermediate in time between the triangular backstamp, above, and the horizontal backstamp, below.
 
WMF newer, horizontal backstamp.
The "new, horizontal" backstamp
 

Backstamp on a piece of ALPHA.
 

Backstamp on a piece of ACTION.
 

Backstamp on a piece of LINEA.
 

Backstamp on a piece of NORTICA.
 
Current WMF backstamp.
Backstamp on a piece of SOLID, a current pattern still in production.
The place of manufacture is not indicated.
 
WMF backstamp on hollow-handled knives.
The "triangular" backstamp found on the handles of hollow-handled knives.
 
'Twins' mark on WMF knife blades.
The "Twin" mark ("Zwilling" in German) found on the blades of WMF knives indicating the blade was manufactured by J.A. Henckels of Solingen, Germany.  So far, I've seen it paired only with handles bearing the triangular backstamp.
 
INOX mark on WMF knife blades.
"INOX" stands for "inoxidable," a general term equivalent to "stainless" in the U.S.  So far, I've seen it paired only with handles bearing the triangular backstamp. 
 
New WMF GERMANY mark on knife blades.
I've seen this blade stamp paired only with the triangular stamp on the knife's handle.
 
This stamp is found on the knife blade of vintage WMF silverplate patterns.  The pyramid with the cross is the logo of the Hammesfahr Nirosta-Werk in Solingen, Germany.  Nirosta is the trademark of stainless made by ThyssenKrupp (now Outokumpa Nirosta GmbH).  The stamps on the handles of these knives are usually an ostrich in a rhomboid or WMF in a square, on one side, and the silver thickness (e.g., 90) in a square on the other side. 
WMF HOTEL

WMF has made and still makes a number of patterns specifically for the hotel, resort, and restaurant trade where durability is paramount.  I have examples of patterns that are currently in production, and nowhere on them is the place of manufacture indicated, so I presume it's not Germany.

This is a backstamp found on a spoon (AKROPOLIS):

Current WMF HOTEL backstamp.

This is the stamp found on the blade of a knife (AKROPOLIS):

Current mark on WMF HOTEL knife blade.
Like most stainless manufactured for hard use, the knife is solid-handled, not hollow-handled.  It does not bear a stamp on the handle, only the one on the blade.
Some WMF Stainless Holloware Backstamps
Links to WMF Marks at