VGFacts

Inside the basement of the Captiol Post building located in L'Enfant Plaza, there is a corpse named "Gibson". Gibson's inventory has four items, two of which are “Gibson's Key” and “Gibson's Scrap of Paper”. The scrap of paper has the following message, "Search the house!"

This references an early scene in Snatcher where the player finds Jean Jack Gibson’s corpse and discovers a key and a scrap of paper with the “Search the house!” message among his belongings.

Here are some screenshots to support this trivia:
(Warning these screenshots are NSFW)