I believe the consensus at WP:USSTATION was that article titles indeed should not be based on signage. However, what matters here is not the formal names of the station, but what they are referred to as in reliable sources. Here are just a few of many examples of the California stations being referred to as "Pomona Metrolink station", including by Metrolink itself as well as by LA Metro, one of Metrolink's governing agencies:      Regards, (/)