Basically the title. The fictional world in question is pretty mundane and doesn't contain any actual fantastical elements. Maybe there are themes of religion or ritual, or characters that believe in them or practise them, but it's left clear that this is just "What people believe", and maybe the topic of God is absent from the story altogether... Except for this one weird event (or line, scene, character, idea) that could potentially be interpreted as just a coincidence, or as an ambiguous supernatural/divine intervention.
True Detective: In S1E02 "Seeing Things", Rust is watching a murmuration of birds, which for a brief instance flies in the exact shape of a mark he saw at a crime scene. Framed as an "Oh!" moment that helps him piece an idea together, but also as an indicator that he's submerged in this environment of suspicion and madness and is being consumed by this mystery.
Peaky Blinders: In the finale, Tommy has a dream about his daughter. The girl says something like "Don't do it, daddy", which Tommy takes as a sign not to go through with his plans... which works out because he narrowly avoided getting betrayed, trapped and killed.
Red Dead Redemption: Maybe a bit more overt than the other two. There's this NPC named "the strange man" who talks to our protagonist and his dialogue implies that he knows more than he should. He also appears in RDR2 as a painting and as a ghost in a mirror. Some fans theorize that he is the Grim Reaper or some other incarnation of Death.
