The law states
Concealment is a broad concept. You and I could debate endlessly about where the line is exactly, but if the intent is obviously to mislead people into thinking that the container doesn't contain firearms, the there's no debate anymore. Burying an "armes à feu" sticker behind a font and a bunch of stickers shows your intent is to hide the fact that there's firearms in that container. Just like a sticker that says "firearm" but in sanskrit or using a cyrilic alphabet of some sort. The guitar/violin shape of the container shows that intent too, compared, to, say, a rectangular plano case. You even say yourself that your intention is to be discreet.
The fact however is that there's little case law about concealed weapons in the context of a RPAL holder transporting legal restricted firearms. The closest is Felawka, but the case is about a guy carrying a NR rifle, loaded, not trigger-locked (or locked in any way at all), hidden in his trenchcoat, in public transportation, more than 25 years ago. It doesn't say anything about the size of fonts or if a picture of a gun on a case would be a sufficient indication that a weapon is contained in there, therefore not concealed. It is kind of obvious to me that transporting firearms (or any weapon) in a violin case is an attempt at concealing those firearms, regardless of any sticker. A judge might say otherwise, who knows.