I’m pretty sure those were actually “FAST”-branded FCI MS-6s, as detailed in this topic: FAST? - Fire Alarms / Fire Alarm General Discussion - The Fire Panel Forums FAST merged with Edwards in 1992 to form EST. Here’s a picture of one such MS-6: FAST-Fire-Alarms-Systems-Technology-MS-6-Non-Coded.jpg (300×400) (picclickimg.com)
