What is this magical posture all about?

Dean Stockwell makes this gesture in the ceremony he conducts in The Dunwich Horror.

https://teleportcity3000.files.wordpress.com/2008/10/dunwich10.jpg

The Occultist and Black Magician, Aleister Crowley, was also photographed doing this gesture.

https://i2-prod.birminghammail.co.uk/incoming/article6833708.ece/ALTERNATES/s1200c/PM2636718.jpg

My guess is that it's a Satanic gesture intended to imitate the look of a ram's horns.

https://www.thetaxidermystore.com/media/catalog/product/cache/1/image/9df78eab33525d08d6e5fb8d27136e95/c/o/corsican-ram-horn-taxidermy-mount-_11646-for-sale-_-the-taxidermy-store.jpg