I haven’t found a sigil for Hekate, interestingly.
You sort of see a beautiful forest, follow the white rabbit to her and her dogs…and she comes alive.
Candles I would say are very nice to use in general, though.
You sort of evoke her with feelings.
Last time I did it, actually, it was the weirdest thing… I called her during sleep. I usually don’t do that, and I wouldn’t even know how to tell you how!
But look at @C.Gren’s description of Hekate… just similar imagery and repeating her name will bring her to you.