The OGC compliance website provides automated tests for Web Map Service 1.1.1 (WMS) and Web Feature Service 1.0 (WFS), and a Geography Markup Language (GML) validation tool with links to reference implementations. Developers that successfully test for specification compliance can apply for formal OGC certification. Once granted, developers can affix the "Certified OGC Compliant" seal on their products and marketing materials.
Compliance testing determines the ability of a product to properly support all mandatory elements of an OpenGIS Implementation specification. Only products that have successfully passed a test, and fulfilled administrative requirements for certification can include "Certified OGC Compliant" mark. Products that have not gone through this procedure, but include support for a specification, are said to have "implemented the specification," and cannot claim compliance.
Source: OGC, Feb. 20, 2004