They have ranged from the commonly used variety - like moving averages, crossovers, the VIX, death crosses, and Bollinger Bands - to the esoteric, including the tallest buildings, Big Money Polls, financial astrology and, more recently, magazine covers.
You'd think the tools market technicians typically use would generate the most interest. But inevitably, it's the more unusual indicators that people are most attracted to.
Why?... I have no idea. I am not a social scientist.
But I can tell you this - having spent tens of thousands of hours computer modeling almost every indicator you can conceive of, the most consistent and best performing indicators are almost always behaviorally-based.
What I mean by that is that there is inevitably an element of human behavior that is either: a) responsible for the indicator itself; or b) contributes significantly to how it functions and why it's relevant.
My grandmother, Mimi, a seasoned successful investor in her own right after being widowed at a young age, used to chalk this up to what she called the "complexity problem" - as in, if it's too complex for me to understand, it's a problem.
She didn't use the term like I do today in a non-linear sense. She simply reasoned that if something was too complex to explain to her, it wasn't worth her time or her money.