H.P. Lovecraft wrote about the Elder Sign in The Shadow Over Innsmouth and The Dream Quest of Unknown Kadath. The elder sign is used in defense against the Deep Ones, they can not harm someone protected by the Elder Sign. The pendant features the handwritten symbol that HP Lovecraft included in a 1930 letter to Clark Ashton Smith.
Details: The Elder Sign pendant is sterling silver with an antiqued finish. The pendant measures 27.5 mm long, 17.2 mm wide, and 1.3 mm thick. The pendant weighs 3.9 grams. The back of the pendant is textured and stamped with our makers mark and metal content.
Chain Options: 24" long stainless steel curb chain, 24" black leather cord (additional $5.00), or 20" 1.2 mm sterling silver box chain (additional $25.00). Additional chains are available on our accessories page.
Also available in enameled sterling silver - click here - and gold options - click here.
Packaging: This item comes packaged in a jewelry box.
Production: We are a made-to-order company. Your order will ship in 5 to 10 business days if the item is not in stock.

Exactly what I was looking for.
I wanted a sterling silver Lovecraft elder sign, not Dereleth's, and this one is perfect. I received it today and I couldn't be happier with it. It looks better than what is shown here.