That has already been defined as something like a ColdCard or SeedSigner. You’d have to include software on a phone or computer in this, so it’s hard to define what the “device” is. That term works for specialized single-purpose devices not more general ones.
Discussion
Who cares, thought the point here was to take ownership over the terms used. Make up a term and stick to it until "they" start using our terminology.
Signing device, signing app, private digital asset safe/secure vault, private digital asset secure manager, etc etc
Make up shit and then own it!