Ooohhh I love adding hidden details among regular items my comic actually has a lot and some are pretty hard to find, or often associated with hidden messages but these are some examples/details that are pretty obvious and some foreshadows that pretty easy to figure out (for me)
1. you can identify whose titled noble's property it is by looking at the flower decor because these flowers is actually a part of their crest/signet. It is usually at wall near the roof of their house/property
2. You can identify who will entertain you as a guest in a noble house base on the tea cup that they present their guests with, because like the roof, the host's tea cups even have the same element of their crest in it, and if you as a guest was presented by it, it means that the host/head will personally meet you
Foreshadow: When Siran, attended the auction, he waited in a room and thought that he will meet the host of the house (which is why he exclaimed that the host of this house is 'welcoming in this panel) little does he knows, the tea has something in it which is why I as the creator, focused on shot of the tea and pastries on the table

3. The masked man aka Valentin already knows something, which is why he confidentally change someone's plan to hand over Siran to him the last minute, and decided to auction Siran instead and was sure that the duke will attend
which is later supported by the evidences from chapter 2 where the duke looks like he received only one letter...
but was later revealed on chapter 14, there was a small note card. And what's was written? "You will find what you're looking for in the auction" which that this note sent by Valentin is the actual trigger for the duke to attend that auction
There's actually one foreshadow that has something to do with symbolism and secret messages but it will be a huge spoiler so that's all I can provide for now ^^