I would think you could name it whatever you want. As long as you don't affiliate it with where it comes from. Such as all the twilight soaps I see. If someone wanted to name their soap Team Edward or whatever, they should be allowed to as long as it is not referenced to the twilight book series or movie. For all anyone knows, the soapmaker's name is Edward and it's his team's soap or something.
I saw on Etsy someone started a thread in the forum saying they got a cease and desist letter from twilight ONLY because she said in her description "I was inspired by twilight" as in the book/movie. And I believe thats the part that got her in trouble. Not because she named her soap Twilight.
But this is just what I think. What I've heard. I don't sell, so I don't have to worry about these kinds of things haha. But there are a lot of Lawyers out there that will give free consultations if you would like to get a definite answer. Hope that helps.
Edit: Hmmm. Or I was just thinking... you could give some kind of disclaimer: "My soap is not affiliated with such and such."
When I search for music on Youtube, a lot of time the music company has had Youtube mute the video because they are using a company's music without permission. People have now started putting disclaimers in their video descriptions saying "I do not own the song. It belongs to so and so. blah blah" Really short litle disclaimers. And as far as I can tell, the music companies have not muted any more videos that have the disclaimer.
Oh and Wholesale supplies plus has "Compare our fragrance to so and so's fragrance" selection. They call it the exact same names and even reference that their fragrance oils smell like bath and body works' for example. But they do put a disclaimer that they aren't affiliated with bath and body works.
Just throwing my thoughts out there. But I would diffidently recommend that you ask a lawyer though. (Some will just tell you your answer for free!) These are just *my* thoughts on this.