No, you don’t, a person does not have to have a sigil of a spirit to call them. That is just a method that you use. Sigils are not medatory, if that was the case, people would not have success with the Practical Jinn Magick. which uses no sigils at all. I was like that too, until I started working with the 360 Jinn from Nineveh Shadrach they do not have sigils and only chants, from then on I just called entities without sigils. Even when I had sigils, I wasn’t bothered to use them, however, I sometimes tell the consciousness of the sigil to open up and flood the room with the energy of the realm of the spirit.
Incense and offerings are also not necessary according to that same book, matter of fact, if you do not raise a proper sacred space, which I do not hear you talking about. You run the risk that wandering spirits, impostors, or parasites take the offer, which is the incense or other offerings you mentioned. *if you do not raise a proper sacred space, you run the risk of evoking an impostor or parasite. Don’t take my word for it, you can read all about it on the forum.
Look, offerings are fine tho, but they are not mandatory at all. You can just tell the spirit to take a bit of your life force to fulfill the request.