Campus administration says theater Prof. James Miller's poster of the TV program's character, which reads "You don't know me, son, so let me explain this to you once. If I ever kill you, you'll be awake. You'll be facing me. And you'll be armed," implies violent threats, the Milwaukee Journal Sentinel reported.
The poster, which also features the "Firefly" character Malcolm "Mal" Reynolds, was removed from Miller's office door.
UW-Stout Police Chief Lisa Walter e-mailed Miller saying "it is unacceptable to have postings such as this that refer to killing."
"It's absurd to say that a reference to violence is some kind of threat," Miller said. "It was a real overreach."
Miller then put up a poster with a headline reading "Warning: Fascism," and features a pictogram of a police officer hitting a person with a baton.
"Fascism can cause blunt head trauma and/or violent death," the poster reads. "Keep fascism away from children and pets."
That poster was also removed.
The Foundation for Individual Rights in Education sent out a newsletter about the incident, which prompted the actor who played Mal, Nathan Fillion, to send a message via Twitter about Miller's struggle with the school administration.
More than 400 people had sent e-mail to the university by Tuesday saying administrators should apologize to Miller.
"We have a responsibility as a university to provide an atmosphere for our students, faculty and staff that is safe," said a university spokesman.