NOTE: It seems this solution doesn't work anymore, at some point FromSoftware patched this. I'm no longer having issues at all (so maybe they fixed something?), but from what I understand some users still are. If your'e unsure, an easy way to check is to get the Watchdogs covenant and get to Farron Woods at a fairly low level (I think around 30). Use the new indicators to see when most of your player summoning range is around there. If you don't get summoned, it's still bugged :(
Dark Souls 3 for PC is broken. At least, it's covenants are.
Since release, the Watchdogs of Farron, Blue Sentinels, and Blades of the Darkmoon covenants have not functioned properly. Where they are supposed to auto-summon you into other peoples worlds under certain circumstances, these tend to not do anything at all. You could wait for hours in Farron keep and never be summoned as a watchdog.
For a lot of people they work fine. In fact this has led to arguments between people for whom it works and doesn't work, with the working people believing the players are too high leveled, or are not patient enough.
However I believe there is definitely a problem with some peoples games, and it appears to be Steam Account related.
A discussion thread on the Steam community has found a temporary fix for getting your character's covenants to work again. Essentially, you have to make a new Steam account and Family Share your library with it. When you play Dark Souls 3 in the new account, you'll be able to use the covenants!
There's an easy way to "import" your save files to the new account so you can play with your old character. If you're looking for achievements (like getting all the rings or spells), you can later transfer your character back to your main Steam account and get those achievements unlocked. I'm not sure if they would activate automatically or if you'd need to pick up one more ring/spell to trigger it, but worst case scenario you just drop your ring and pick it back up.
Here's a video on how to transfer your character:
Check out the full Steam discussion below:
To be honest I didn't quite believe this would work, so I tried it for myself. Unfortunately I was already on New Game + with my main account so there didn't seem to be much of a summoning pool. I did sit in Farron Keep for a bit and got two summon attempts, but both failed due to connection errors. To be fair nothing like that had ever happened before while I had the Watchdogs covenant on, so it was indication that the fix worked. But that wasn't enough proof for me.
I started a new character and worked my way back to Farron Keep. Two hours later, I had the covenant and I waited by the bonfire.
And lo and behold, I got summoned! Here's proof!
So there you go, this fix works. This is also good indication that something is seriously wrong with certain people's games, some sort of account confict. It's very weird because the other auto-summon covenant, Aldrich Faithful, works just fine!
I will say, I've been noticing less summoning signs than I remember there being... But then again, it's been a month and a half since I played, and I've been keeping my soul count much lower than last time (and haven't upgraded any weapons), so maybe I'm underleveled? I'll have to test this further by grinding a boss or something.
I hope that From Software does something about this problem soon. Honestly I had stopped playing last month after getting discouraged from the covenants being broken and being locked out of those gameplay experiences.