Identifying custom or less common applications running on standard ports is a key use case for App-ID's custom application signature capabilities. Option A correctly describes the process: create a custom App-ID signature that looks for unique attributes of the application traffic (like specific HTTP headers, URL patterns, or payload content that identifies it as the custom app), and then use this custom App-ID in security policies to apply granular control and inspection. Option B is incorrect because modifying default signatures is not possible or recommended. Option C is incorrect; Content-ID focuses on threats and sensitive data within applications, not the identification of the application itself. App-ID is required for application identification and policy enforcement. Option D is a workaround using URL filtering but doesn't provide true application-level identification and control based on App-ID. Option E is impractical and defeats the purpose of a unified SASE architecture like Prisma Access.