Though Miser often over-reacts to, well, a lot of things, I do find it odd that +Vigano would use this phrase (if it can be called that) to end his communication with. Hopefully it is a mistranslation. In doing a google search, I can't find that Catholics use this phrase.
This phrase simply means "Amen", or could also be a traslation of "Deus vult", and people have to recall that +Vigano is Italian, so that it's likely some Italian expression, or could just be an over-zealous translator over-translating "Amen" (which basically means the same thing, so be it). Or it could even be a translation of "Fiat" (echoing Our Lady's "Fiat"). Masons also use "Amen", so now if someone uses "Amen" he's a suspected Mason?
Still not a single convincing explanation for what "harm" +Vigano is doing or what their purpose might be to roll out a +Vigano. Really, the biggest effect he's had is to bring some conservative Novus Ordo types to the right, people who formerly were afraid of criticizing Vatican II or Bergoglio. He's swung to the right of the neo-SSPX. He's not "converting" any sedevacantists or Traditional Catholics, nor ordaining dubious priests. He hasn't set up some kind of rival seminary. He hasn't even gone after sedevacantists. If I had see him writing some attack against sedevacantists, I might even find the assertion plausible that he was being set up as some kind of "gatekeeper". But, if anything, a lot of what he rights could be considered a "gateway drug" to sedevacantism. He regulalry refers to a Bergoglian sect (vs. the Catholic Church), and has made similar comments about the entire Conciliar Church before Vatican II. I have not seen a stronger or more articulate condemnation of Vatican II and the NOM from Archbishop Lefebvre.
I have the same issue with those who claim that +Lefebvre was "controlled opposition". Nonsense. Had +Lefebvre not been around, the Traditional movement wouldn't be 1% of its current size. So what did he accomplish for the opposition?