Made by casting with artificial patination (dark coating).
Usually metal wreaths goes with the same eagle insignia, together they made up the set of insignias for the peaked-cap of the Heer. There were also embroided signs during WW2. Both metal and embroidered signs for officers' peaked-caps were equally common in the Heer.
How to install the insignia? Put the sign to the cap so that it sits well. Open the legs and put again. Mark with chalk or felt-tip pen the places where the legs stay. Poke holes for the legs in the cap with an awl, being careful not to pierce the lining and leather tape from the back. Put the legs into the holes and press the sign, gradually bending the legs, without grabbing the lining with the legs. The legs should remain under the lining.