From older sources, we find that Sif is a swan maiden and can shape-shift into this form. Having previously been married to Orvandil, she is viewed as one of the older race of gods.
Sif signifies summer fertility, and corn. Thus the following tale of Sif and Loki:
An incident occurred, while Thor was gone, in which Loki sneaked into Sif's bedroom and cut off all her beautiful golden hair with a sharp sword. Sif's hair representing harvest, corn, abundance and prosperity.
Thor was furious at what Loki had done to his wife's hair. So with Thor's threats ringing in his ears, Loki went to the sons of Ivaldi who made magic hair made of "gold" for Sif, the spear Gungnir, and the ship Skidbaldnir. Some translations call these craftsman Elves and other Dwarves.
On his way home Loki met two other craftsman, Brokk and Eitri, who were kinsmen of Sindri, a second family of Elf-smiths. Loki bet his head against their ability to make equal or better gifts.
Brokk and Eitri forged Odin's arm-ring Draupnir, Thor's hammer Mjollnir and Frey's boar Gullinbursti. The gods decided that the gifts were as good as the first ones, and Brokk demanded Loki's head. Cleaver Loki agreed, but said Brokk could have none of his neck. So Brokk settled for sewing Loki's mouth shut. The other God's laughter at Loki's pain made Loki decide to plot revenge.
Sif is the goddess of peace, friendship in a happy family. She is chaste and is associated with "Kin" or "Kindred." The runes compatible with Sif are Berkana and Inguz.
May the Blessings of Sif be yours,