I started with a Dollar Store sign. That way I didn't need to cut anything out. (Please excuse the horrible pictures)
I spray painted it black...
then I sanded it to let a little of the green show through.
Next I took some vinyl and cut out the lettering. "Humans who dare enter will be chained and tortured" I bought some fake chain from Walmart and hung it on the door first. Then I hung the sign and added some black cheesecloth and spider webs. Perfect for my front door.