They own it, sure, but they license it out freely. They've released their work under a license that allows anyone use of their trademark, as long as they stick by the AGPLv3. The AGPLv3 is written permission.
I think what Signal is objecting to is that the snap looked like it was packaged and distributed by Signal when the files included could have been modified with a backdoor or whatever.
https://github.com/signalapp/Signal-Desktop/blob/main/LICENS...
I think what Signal is objecting to is that the snap looked like it was packaged and distributed by Signal when the files included could have been modified with a backdoor or whatever.