It seems germane to here mention how in this version of Golarion everyone can tell when a spell is being cast in front of them, but not necessarily what that spell is.
Korvosa, being a city where wizards carry cultural cachet, has no strong norm against casting spells in public--but it's the kind of thing that, depending on context, might make people antsy or prompt a bodyguard to attempt interrupting the spell. It's polite and helps avoid misunderstandings for a wizard to say "I'm going to cast prestidigitation" before doing so, or to simply step out of the room for a moment, since for all anyone without ranks in spellcraft knows you could be planning to cast almost anything.
This is why the Arkonas, in setting up their message relay, relied on the long range of the spell; anyone in the relay without one feat or another to cast surreptitiously first slipped out of sight, and they did all the finger-pointing too.
This hasn't seemed important to note before, but while I know I had it in mind as a constraint earlier on in the scene it must have slipped my mind by the time Glorio and Ileosa cast message on each other in public (Glorio probably has some trick to cast without making it obvious (not in his printed statblock from 3.5, which is mainly what I've been using for him. Nonetheless.) but wouldn't want to demonstrate it) which made me think I should write this down explicitly.