A separate Sending outlet for the Watcher barracks might be a bit much, but how about an NPC courier or errand boy who for a payment of 15 gold (5 or for free for sergeants/officers) would run to the Herald and pass on Watcher Sendings for the Watchers?
I love this suggestion. Make that secretary do her job!
It's been a long time since I've played a Watch PC, but can't you already get any Watch NPC to file a location-based report that pings every Watcher online? That still worked the last time I tried it in EfU:R. Just ask the NPC to "file a report" and sooner or later a PC will show up.
There also used to be a way for Watch PCs to ping other Watch PCs to come to their location. Not to get too spoilerish, but if there's some reason those tools aren't still in use, it's probably not for an IC reason. Watch PCs still had them during the fall of Sanctuary, we just stopped using them because they made no sense on the Archipelago. Maybe the DMs can bring that system back if it isn't already in use.
The report system is in, but when you need to summon people to the Watchhouse it'd be great to have a courier in there. Maybe a Watcher Recruit NPC who's under some perpetual punishment.
Could push for this in game too...