Loki, by Mårten Eskil Winge 1890
Sigyn (Old Norse "victorious girl-friend") is a goddess and wife of Loki in Norse mythology. Sigyn is attested in the Poetic Edda, compiled in the 13th century from earlier traditional sources, and the Prose Edda, written in the 13th century by Snorri Sturluson. In the Poetic Edda, little information is provided about Sigyn other than her role in assisting Loki during his captivity. In the Prose Edda, her role in helping her husband through his time spent in bondage is stated again, she appears in various kennings, and her status as a goddess is twice stated. Sigyn may appear on the Gosforth Cross and has been the subject of an amount of theory and cultural references.
Sigyn is attested in the following works:
 Poetic Edda
In stanza 35 of the Poetic Edda poem Völuspá, a Völva tells Odin that, amongst many other things, she sees Sigyn sitting very unhappily with her bound husband, Loki, under a "grove of hot springs". Sigyn is mentioned a second (and final) time in the ending prose section of the poem Lokasenna. In the prose, Loki has been bound by the gods with the guts of his son Nari, his son Váli is described as having been turned into a wolf, and the goddess Skaði fastens a venomous snake over Loki's face, from which venom drips. Sigyn, stated again as Loki's wife, holds a basin under the dripping venom. The basin grows full, and she pulls it away, during which time venom drops on Loki, causing him to writhe so violently that earthquakes occur that shake the entire earth.
 Prose Edda
"Loki Bound (motive from the Gosforth Cross)" (190 by W. G. Collingwood.
Sigyn appears in the books Gylfaginning and Skáldskaparmál in the Prose Edda. In Gylfaginning, Sigyn is introduced in chapter 31. There, she is introduced as the wife of Loki, and that they have a son by the name of "Nari or Narfi". Sigyn is mentioned again in Gylfaginning in chapter 50, where events are described differently than in Lokasenna. Here, the gods have captured Loki and his two sons, whom are stated as Váli, described as a son of Loki, and "Nari or Narfi", the latter earlier described as also a son of Sigyn. Váli is changed into a wolf by the gods, and rips apart his brother "Nari or Narfi". The guts of "Nari or Narfi" are then used to tie Loki to three stones, after which the guts turn to iron, and Skaði places a snake above Loki. Sigyn places herself beside him, where she holds out a bowl to catch the dripping venom. However, when the bowl becomes full, she leaves to pour out the venom. As a result, Loki is again described as shaking so violently that the planet shakes, and this process repeats until he breaks free, setting Ragnarök into motion.
Sigyn is introduced as a goddess, an ásynja, in the Prose Edda book Skáldskaparmál, where the gods are holding a grand feast for the visiting Ægir, and in kennings for Loki ("husband of Sigyn", "cargo [Loki] of incantation-fetter's [Sigyn's] arms", and in the 9th century Haustlöng kenning "the burden of Sigyn's arms"). Sigyn's final mention in Skáldskaparmál is within a second list of ásynjur found in chapter 57.
From: WikiSigyn (pronounced SEEG-in) is the Norse Goddess of fidelity and devotion. She is the wife of Loki, and she watches over him in his captivity. After Loki orchestrated the death of the God Baldr, the Gods captured him and his two sons by Sigyn, Váli and Narfi. Váli was transformed into a wolf, and he then turned on his brother and killed him. The Gods then used Narfi’s intestines to bind Loki to three rocks, and the Goddess Skaði places a poisonous snake over his head. The venom from the snake drips down towards Loki, but Sigyn catches it in a bowl to save him. When the bowl is full, she must turn away to empty it, and the drops that fall on Loki cause him such pain that he thrashes violently, resulting in great earthquakes. Loki remains bound with Sigyn by his side until Ragnarök, the Twilight of the Gods. Sigyn’s name, which means “victorious girlfriend,” is also seen as Signy or Siguna.
From: hereFrom here: SigynHer name, appears to etymologically derive from two Old Norse words, sigr (victory) and vina (meaning girl-friend). This will cause some modern-day practitioners to hail Her in rites as “Victory Bringer.”
Appearances in Lore: Volupsa, Gylfaginning, Skaldskaparmal, Haustlong, Pulur, Þórsdrápa
she was counted among the Asyngr (the name given to the Goddesses among the Aesir).
She was wed to Loki, and with him had two sons
As described in the lore, Loki’s two sons were slain, one forced to kill the other. The intestines of her son was then used to bind Loki. Sigyn stood at his side in her grief, and held up a vessel to catch the poison that burned like acid, that dripped from the snake fixed above Him.
One of her by-names, or kennings is “Incantation-Fetter” (used briefly in passing in Þórsdrápa).
Because she’s mentioned in Haustlong (an older text and one of the few actually written by a pagan skald, and not a Christian scholar) I’ve seen scholary theory that she may be a Goddess from the older Germanic tradition, which carried into the later appearing Norse culture.
Appearance in Archaeology: Outside of these references in the ancient lore, we do have one believed artistic depiction of her in archaeology, specifically on the Gosforth Cross depicted in conjunction with a bound Loki (the art is very primitive and certainly not detailed).
From, for the rest go here: Wyrd Designs – Exploring Our Gods And Goddesses – Sigyn
Gangleri's Grove -- Galina Krasskova's section for Sigyn (& Loki) related posts
Shrine of Sigyn -- From the Northern Tradition Paganism-- has some essays, prayers and such
Temple of the Flea -- Sigyn page
Deity of the Month: Sigyn -- has info about her
From Odin's Gift (submitted prayers, poems and writings):* Sigyn Talks Laura GjovaagLoki and Sigyn's First Meeting
* Sigyn´s Song Galina Krasskova
* Sigyn’s Song Mikki Fraser
* Sigyn´s Angst Tracy Nichols
* Do Her Cries Fill Your Ears? K. C. Hulsman
* Honoring Sigyn Sophie Reicher
* Acrostic for Sigyn Galina Krasskova
* Prayer for Sigyn Galina Krasskova
* Litany for Sigyn Galina Krasskova
* Prayer to Sigyn Galina Krasskova
* Sigyn - My Lady of Blue Petals Salena
* Vigil Speak Salena (disclaimer: strong language)