Sioned is the Welsh form of Janet — itself a diminutive of Jane, from the Hebrew Yochanan meaning "God is gracious."
Sioned is widely used in Wales.
Sioned 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.
In Pythagorean numerology the letters of Sioned reduce to 3, The Communicator. This is a traditional interpretive system, not a factual claim about the name.