MTS Model FlexTest SE - Manual (Page 146)

Models FlexTest® IIm/GT/SE Controller Hardware
Workstation Connection
FlexTest GT Controller Connections 146
The symbol shown here indicates that you must not connect
telecommunications equipment to the equipment showing this symbol.
Several modules have connectors that look similar to a phone connector. Special
cables are required. Installing telecommunications equipment cables can cause
equipment damage to the electrical components of the chassis or to your
telecommunications system.
CAUTION