[caf]

Enabling the advisory mode by default seems like a mistake, at least with the current UI. It is so unobtrusive that it carries a very distinct implication of "we've looked into this for you, and you don't need to worry about it", which is not the case. The iconography of the shield also implies this - it says "Signal is protecting you".

The message probably needs to be more explicit: "Voltairine de Cleyre isn't using the same safety numbers anymore. Probably this contact just has a new phone or reinstalled Signal, but you might want to confirm the new safety numbers with them.". And the accompanying icon should be an ! or ? or something.

[chrisfosterelli]

Yeah, while a security conscious user would probably be curious about this and investigate, I think an average user would just ignore it.

I've been talking with people who haven't noticed when I change the disappearing messages on/off, which has the same appearance and displays in the same place as these advisory messages, so clearly some people are already ignoring them.

[nullc]

"Your correspondent had been replaced by a man-in-the middle for you convenience. Have a nice day."

[grrowl]

I agree on both points. Muted red text and a broken/unlocked padlock would convey the intent a lot more clearly.