Use a "buried electric line below" sign.
Size: 7" x 10" Material Type: HDPE Plastic Sign Verified Purchase
Size: 3.5" x 5" Material Type: Reflective Adhesive Signs and Labels Verified Purchase
Size: 7" x 10" Material Type: Aluminum (40 mil) Verified Purchase
Size: 5" x 7" Material Type: Reflective Adhesive Signs and Labels Verified Purchase
Very happy.
The labels were exactly what I needed, service and delivery were great.