One thing I really love about Darkest Dungeon is how aesthetically consistent it is. The symbol displayed in the launch announcement to the left is a reoccurring visual motif throughout the game. Of course, since it seems to be the mark or sigil of the eldritch evil affecting the setting, you'd expect it to be prevalent in the game, but is also shows up in a variety of more subtle ways in addition to the cultists' decorations:
Keep an eye out for that symbol in background elements, doors, weapons, clothing elements, wheels, enemy powers, various detritus, etc. Some examples:
The prevalence of that symbol, or at least of allusions to the symbol, do more than just add aesthetic consistency to the game. In a subtle way, it illustrates one of the themes of the game: the eldritch evil that the symbol represents is pervasive and has invaded the very fabric of the setting's reality.
That's a technique worth stealing for role-playing games, by the way: if you want to reinforce an idea or theme in your game, insert it in a wide variety of forms; make it reoccur so that it can't be ignored; put it in the background and let the players pick up on it as the game moves forward.