As we all know the Watchers have their bounty board of npcs and a sending is made for each one that shows up. The same goes for Aberrant bounties for the Society (Or did) but they had a special announcement for it.
I feel the Spellguard should have something along the lines like this to make it a more interesting faction and make it seem like more is being done to lower the number of chosen in the machine. Also gives the players in the Art of War school more reason to patrol the machine on a daily basis and bring some other players along with them. The rewards could be simply some gold, or spellguard cares healing tools or perhaps a trinket.
This is a good idea and could be expanded to include some large rogue animatrons of unusual design or power, dangerous scrapper saboteurs or anti-machine wildlings tampering inside the Machine.
I honestly think if there were a Chosen bounty in place it should exist in lower. Upper has a bounty system already via the Watchers. Winston paying bounties for Chosen who steal children in the night seems real and balanced.