Monitoring Systems of both Internet applications and services are, nowadays, a rich source of information and an agile decision support tool for System Administrators. In environments with a high access volume and hundreds of servers, to communicate abnormal events in an interface accessible through a Web browser is considered a big interface design and interaction challenge, particularly in situations where information and decision-making are critical. Given that, the main focus of this work is to study monitoring systems in a big Brazilian Internet company. We begin with a detailed evaluation of systems used in the company and then we elaborate, implement and evaluate a new design model that we propose for similar monitoring systems. This new model demonstrates how the Semiotic Engineering, a semiotic theory of HCI, can be combined with elements of a human-factor and ecological psychology design theory, the Ecological Interface Design, in order to elaborate the communicability and build interaction for monitoring systems. The combination of both approaches provides certain characteristics of representation and communication that, according to the evaluations conducted in this research, the decision-making support becomes both increasingly efficient and agile for the users in such domain.