The HP Engage Flex Pro G2 is the recommended system for a customer looking for a product with a compact design that can support multiple displays for digital signage. This system is designed to offer high performance and flexibility in a compact form factor, making it ideal for environments where space is at a premium. It supports multiple display outputs, allowing it to drive several screens simultaneously, which is crucial for digital signage applications. Reference for the HP Engage Flex Pro G2's capabilities and specifications, including its support for multiple displays, can be found in the product datasheets and technical documentation provided by HP.