Letters of Note has letters from Phillip K. Dick to the FBI and the county sheriff’s office about plots by Neo-Nazis to insert coded phrases into Science Fiction. He even claimed that Thomas Disch’s book Camp Concentration had some of these phrases.
Phillip, of course, was not well and was probably schizophrenic. (He was never actually diagnosed, but these letters exhibit behavior that is not normal.)
The coded information which Kinchen wished placed in my novels (I of course refused, and fled to Canada) had to do with an alleged new strain of syphilis sweeping the U.S., kept topsecret by the U.S. authorities; it can’t be cured, destroys the brain, and is swift-acting. The disease, Kinchen claimed, is being brought in deliberately from Asia by agents of the enemy (unspecified), and is in fact a weapon of World War Three, which has begun, being used against us.