As an example, a simple trading system indicator is a moving average crossover. A buy signal occurs when the shorter (faster) moving average crosses above the longer (slower) moving average. A sell signal occurs when the shorter moving average crosses below the longer moving average (a popular combination is a 50-day and a 200 day moving average pairing).
Shorter moving average systems are more timely, generate more trade signals and have more false signals than systems with longer moving averages. Longer term pairings will have fewer false signals but will be late in and late out.
A system like this works well in a trend but poorly when in a trading range. Don't get excited by the prospect of this or almost any other technical analysis indicator. They predict nothing.