I had a question recently about working with a fixed star that wasn't on the 15 fixed stars list. One of the reasons we work with the manuscript Hermes on the 15 Fixed Stars is that we have the fullest amount of information with them, including sigils, in various versions, descriptions of their images, plant and mineral rulerships and best of all, effects.
Of course, all the fixed stars, like all things in the Cosmos, have spirit/angel/daimons. If we knew how to approach them and what they were useful for, we could work with any fixed star or constellation, for that matter.
There might be a way to mechanically generate fixed star sigils, akin to the use of magic squares/planetary tables for planets. More to my personal preference is a more artistic and visionary process, similar to what Jason Miller and his collaborator used for their recent set of planetary sigils in "Advanced Planetary Magic" I like the idea of getting images and sigils directly from the spirits in dreams and visions. But we are going to have to wait for this sort of information until our contemporary visionaries make contact with these spirits.
In the meantime we can certainly use the image of a constellation for a constellation talisman, for Fomalhaut, "the mouth of the fish" a fixed star in the Pisces Australis, the Southern Fish we might use an image of a fish or even an actual picture of Fomalhaut, see Wikipedia on Fomalhaut. This approach, using the planets was followed in Israel Hibner's 1698 Mysterium Sigillorum, Herbarum and Lapidum, "The Mysteries of Sigils, Herbs and Stones." Available at Renaissance Astrology.
I look forward to seeing more visionary art and visionary communication with the spirits of the fixed stars and constellations!