Seamaster caseback with hippocampus medallion

Probable

The Seamaster's caseback carries a seahorse — the hippocampus — as a raised or embossed medallion. It has been executed in several ways across seventy years, from a stamped relief on vintage screw-backs to a sharply defined modern medallion, and the execution is period-specific rather than constant. Its usefulness is asymmetric and worth being precise about: a poorly defined, shallow or misproportioned hippocampus is a strong indicator of a counterfeit caseback, while a well-executed one establishes only that the caseback is good. Casebacks are separable, so the medallion authenticates a part, not a watch.

Part reference

Brand: Omega
Material: Stainless steel, gold or titanium according to case
Identifying marks: Crisply defined relief with even depth across the whole figure. The reference number is stamped on the INSIDE of vintage casebacks together with case-maker marks; modern backs carry model text and, on some, the water-resistance rating.

Documented variations

Classification

FactoryDocumented as shipped from the factory for this reference and period.PeriodNot original to this watch, but correct for its production period.ServiceFitted by the manufacturer's own service network. Not a defect.AftermarketThird-party part. Affects originality, not authenticity.ModifiedGenuine parts in a configuration the factory did not sell. Affects originality and value, not authenticity.CounterfeitDeceptive reproduction intended to pass as genuine.UnknownEvidence on file does not settle the question.

Vintage stamped relief
FactoryProbable
Whole production
Shallower and softer than modern executions by manufacture, not by wear. Do not read period softness as poor quality.
Service replacement caseback
ServiceProbable
Whole production
Omega fits replacement casebacks during service. A replacement carries a correct medallion and a correct inside stamp while having no original relationship to the watch, which is exactly why the caseback cannot carry an authentication on its own.

Documented on these references

Omega CK2913Factory
Whole production
Omega 2531.80.00Factory
Whole production

Provenance of this record

Sources & Evidence

Primary sourceManufacturer archive

OMEGA Vintage Database

OMEGA SA

Accessed: 2026-08-18

Cited for

This referenceProbable

View source ↗

Secondary sourceCollector research

Omega collector research on reference numbering and caliber revisions

Omega Forums and allied collector communities

Accessed: 2026-08-18