MES Systems A5 Metal Warning Sign for Gate Posts. Customers onlyBranded MES System warning signs can be a good deterrent to potential criminal activities by making individuals aware they are being observed and that the system is maintained by a SSAIB approved installer. This particular sign is designed to be fitted on the gate or post next to an automated gate or barrier. It comes with matching screw caps covers. Also, it can be particularly valuable in public spaces, workplaces or residential areas where