What does the flash code of 52 mean on the air bag light for Mercury Grand Marquis 1994?

That is usually an indication that the safing sensor, or the harness between the sensor and the air bag module, is faulty.
The Safing sensor provides back-up power to enable deployment power after main battery power may have been lost (collision event).
Diagnostics on this is tricky, even for an experienced tech.
You should have the concern diagnosed locally by someone with the training and tools to fix it.