Can I tap a Seal for "Sigil of the Storm"?

No, you cannot use a Seal to pay for the recycle cost required by the Sigil of the Storm battlefield.

According to RiftJudge FAQ #6663 and FAQ #8821:

• Sigil of the Storm specifically requires you to "recycle a rune."
• This is a specific game action requirement, not a general "pay Power" cost.
• Seals generate Power, but they do not perform the action of recycling a rune. Because the battlefield mandates the act of recycling, you cannot substitute this with a Seal or any other method of generating Power.

In summary, you must actually recycle a rune card from your rune deck or board to satisfy the Sigil of the Storm requirement.