A few years back a few of us got together to create a jam that answered the question, what if you could only piece together a story from artifacts left behind after the fact. This ended up generating the Artifacts of Horror Jam. There were some phenomenal artifacts created (here) but I wanted to share the genesis document. In it is a list of omens (and corresponding dates) that could easily be used as session seeds for a Liminal Horror adventure, scenario, or session.
The attached pdf has a table of omens and types of artifacts that may have been left behind. There is also a perchance oracle that will randomly generate an Omen for you.