This is the "Do Not Cross" line. The datasheet will list parameters such as:
The includes a mandatory reflow soldering profile. Ignoring this leads to "flux ingress" (contamination inside the relay).
When searching for "TSC-407 datasheet," ensure you aren't looking at the TSC-406 (12V) or TSC-405 (5V). The numbering convention is usually:
The "07" suffix in TSC-407 indicates a . This is a standard for industrial telecom equipment, allowing the relay to be driven directly from 24V rails or via a simple transistor driver.