Diablo 4 hides two Old Tristram achievements that are easy to miss
Talk to Tristram's residents before finishing two side quests to earn both achievements.
Old Tristram has plenty of secrets in Diablo 4 Season 15, from 
Wirt's Lucky Coins to the hidden fight against the Prime Evils. But even if you have finished both side quests and explored the town, you might have missed two small achievements (or challenges) hiding in plain sight.
They are called "Butcher Loremaster" and "Sign Snooper," and getting them requires a little extra work before you finish the quests.
How to Unlock Butcher Loremaster and Sign Snooper
When you pick up the two side quests in Old Tristram, the town's NPCs gain new dialogue options related to each quest. Ogden's Sign asks about his missing tavern sign, and The Butcher asks residents what they know about him terrorising the town.
Your job is to speak to the residents and select the relevant dialogue option for each quest. You need to gather information from everyone before completing the associated quest.
The easiest way to find the NPCs is to check your minimap. They appear as small white dots, making it easier to track them all down.
Once you talk to the last person, the hidden achievements should unlock automatically. You do not need to complete any additional objectives beyond gathering the information.
Watch Out for a Possible Bug
There is one small issue if you have already completed these quests before. It has happened that the game may fail to register the conversations correctly when you repeat them, even if you speak to every NPC.
If you have gone around town and neither achievement unlocks, try creating a new character and starting both quests again. This time, talk to everyone before completing them.
This workaround comes from player reports and not an official Blizzard confirmation, so it may not 100% work. Still, it is worth trying if your achievement progress remains incomplete.
Are the Hidden Achievements Worth Getting?
Sadly, do not expect much beyond the achievements themselves. Neither one grants a title or any additional reward, so this is mainly for completionists who want to finish as many Season 15 challenges as possible.
There is also some uncertainty around how long Old Tristram will remain accessible. Since it is part of Season 15's secret content, it is worth completing these challenges before the season ends on December 1st.
If you have already spent time exploring the town, it is easy to miss. So take a few minutes to talk to everyone before finishing those quests.