What are nymphs?

[Anassa]

Maybe this will give you a clue

Fairies

And in my country we call them Nymphs they were and still are very sacred and plenty of them raised Gods. There are Celestial Nymphs (such as Hesperides and Pleiades) Land Nymphs Water Nymphs Wood and Plant Nymps Underworld Nymphs.

Fairies

Usually they’re more than 2 Not only they’re pure (that doesn’t mean they didn’t had relationships with humans and Gods), they’re great tutors as well, they have been tutoring Gods and heroes after all such as Dionysus, Zeus, Hera, Persephone, Pan, Hermes. Gods were trusting their children to them and cities got names after them. They like dancing and singing, they are known for dancing in the forests along with Artemis and Aphrodite, even Apollo joined them.

Invocation of nymphs?

Nymphs are fae. They will come if they want, when they want and however they want. As nature spirits they have their 2 sides, a very sweet and a very evil one. No sigil for them, but probably you could make one yourself.