Approving a transaction your signing device cannot decode into human-readable terms, so it displays raw data rather than what the transaction will do.
Why it matters
A device that cannot tell you what you are authorising cannot protect you from authorising the wrong thing. A blind-signing warning is information, not an obstacle — it is the device saying its main safeguard is unavailable for this request. See how to read a transaction before you sign it.
What you can check
Signing devices differ in what they can decode. A device that renders the contract call, the recipient and the amount in words is showing you the transaction; a device showing an undecoded blob is not. What the interface displays and what the device displays are two separate claims, and only the device is outside the reach of a compromised front end.
Where it showed up
Records in the Incident Tracker that turn on this: Bybit cold wallet compromise and Radiant Capital signing compromise.
Not advice. Definitions are for understanding, not instruction. Nothing here is financial, legal, tax or security advice.