You're right! This was
Eric Brakken at Glasshouse Studio in Seattle. I emailed the studio and they confirmed it.
They even still make a modern-day version of the same piece: http://www.glasshouse-studio.com/image/99181235.jpg
The WFS is their code for Weight Flat Sided. (Other codes they use include WSF for Weight Single Flower, WRA for Weight Round Abstract, WOA for Weight Optical Abstract, VFS for Vase Flat Sided, VFP for Vase Footed Petite, VFA for Vase Footed Abstract, etc.).
Thanks for helping me solve this glass mystery!