The Yarn (Gimmicks and Online Instructions) by Manuel LLaser - Trick

• The ball of wool is in the spectator's hand since the beginning of the show.
• The bill is really SIGNED by the spectator.
• The spectator himself unties the signed bill from the end of the yarn.
• He also unfolds the bill and checks his signature.
• The ball of wool is in sight the whole time, in a clear glass, while unwinding the yarn.