I played dishonored for 23 minutes and I wanted a souvenir. You bet your whale oil I made one.
Step 1: What you need
Oil clay, plaster, paint, fake leather, hot glue, knife, clear coat and a marker
Step 2: Make a mold
Split the clay in two. One part being significantly larger. The larger half should be rolled out and shaped into a oblong egg shape, add a raised bit to it so the plaster will look cracked. The other piece should be made into a wall to hold the plaster in. Put the finished mold on a plastic bag to reduce the mess.
Step 3: Mix and Pour
Mix just over a fourth a cup of plaster, mix until the lumps are gone, pour into the mold slowly. Make sure it fills completely.
Step 4: Start carving
Remove the plaster from your mold when its dry enough. Sand any rough edges down and mark your lines. Take a knife and cut into the plaster as far as you feel comfortable, just not too deep
Step 5: Base Coat
The first coat is a basic cream color, I mixed yellow, white and some brown.
Step 6: Fill the lines
Use a small paintbrush or a quill tip like I did to fill the lines you carved with black paint.
Step 7: Weathering
Mix some glue, brown paint and water to make a glaze. After it dries add a new coat and make sure you clear coat in-between layers.
Step 8: The symbol
Look at a reference picture (use Google) and paint the trademark symbol onto the rune. Make the lines fairly bold.
Step 9: Leather bits
Cut 4 pieces of fake leather into 1 and a half to 2 inch strips. Glue on on each quarter of the rune.
Step 10: Ta-Da, you're done
You're done, what other explanation do you need :p