What it certifies
The Geneva Seal is the only watch-level certification (not just movement) backed by the canton of Geneva. To qualify, the watch must (1) be assembled in the canton of Geneva, (2) meet a 12-criterion finishing checklist (anglage on bridges, polished sinks, polished pivot ends, jewel countersinking, no visible tool marks, etc.), and (3) meet a timekeeping spec of -1 to +10 sec/day on a cased watch. The hallmark is stamped on the movement and registered with the Geneva watchmaking-school authority.
What's hard about it
Most COSC tests are done on bare movements; many factory-tier Swiss watches pass COSC but couldn't pass Geneva Seal because the finishing on the case-back-side of the movement is industrial, not hand-bevelled. Geneva Seal requires every visible movement edge to be hand-finished, which adds 8-30 hours of labour per watch. The geographic restriction limits which brands can apply: only Geneva-based watchmakers qualify, ruling out makers in Le Locle, La Chaux-de-Fonds, or Glashütte.
Who uses it
Vacheron Constantin, most-prolific Geneva Seal user. Roger Dubuis, every watch they make carries the Seal as a brand requirement. Gérald Genta historically. Cartier (Geneva-assembled references). Most Patek watches qualified pre-2009 but Patek introduced its own internal Patek Seal in 2009 and stopped applying for Geneva Seal certification.
What it costs
Geneva Seal certification is bundled into the brand's pricing rather than visible as a line item; expect 10-25% premium over a non-Seal equivalent at the same level of haute-horlogerie finishing. The Seal itself is not the source of cost; the finishing labour required to qualify is. As a buyer, the Seal signals 'this watch was finished to a specific verified standard, not just claimed to be finished to one'.