Name some unintentionally iconic elements of a franchise, series, etc.
What I mean here is some aspect of a movie, TV series, etc. that wasn't part of the original concept, but became a signature component of the franchise after being implemented due to budget constraints or some other reason. I'll start with this:
Series: Star Trek
Element: The transporter
Reason: Budget and time constraints.
Gene Roddenberry originally planned to depict the USS Enterprise landing on each planet the crew visited, but the continuous utilization of models and sets would have been too expensive. This led to the concept of the small shuttlecraft, but the models and sets for it were still under construction at the time filming had begun. So the idea of the transporter was settled upon, using simple camera fade-out effects and superimposition of the beams of light.
Today, Star Trek just wouldn't be Star Trek without its iconic transporter and the accompanying (misquoted) catchphrase, "Beam me up, Scotty."
What are some other instances of this? (There's another I could mention, but will wait and see if someone else comes up with it).