For future reference:
Demons have sigils
Angels have seals
Deities/gods/goddesses have symbols
and only some deities have symbols, some of which were created by humans like you and I and were not provided by the deity themself. I have never used any symbols when calling upon a god or goddess because there is much confusion there. I usually just use a visual representation of them based on what others have drawn, then once I actually see that deity, I use my own visual representations as well as other items that are known to be associated with that deity such as specific herbs, gems, crystals, metals, etc.
once successful contact has been established, I personally would ask that deity to channel a symbolic image thru you, something that can be used from there on out to contact them. Ask them to create a symbol that can be linked to them and draw it on paper. You can use scrying or various channeling methods to obtain one from them if they agree to provide one.