Sif is the Norse goddess of fertility, the harvest, and family — the wife of Thor. Her golden hair was said to represent the wheat fields; when Loki cut it off, the dwarves crafted her replacement strands of pure gold.
Sif is rare as a given name but rising — propelled in part by the Marvel character Sif (played by Jaimie Alexander in the Thor films).
Sif does not currently appear in the US Social Security Administration's top 1,000 girls' names, so we don't publish a US rank or birth count for it. That says nothing about the name's standing elsewhere in the world — only that it sits outside the ranked US data we rely on.
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In Pythagorean numerology the letters of Sif reduce to 7, The Seeker. This is a traditional interpretive system, not a factual claim about the name.