Three do show a trend. That’s always been a rule. Unless you are talking about something else.
For a symmetric data set (One where negative and positive numbers are possible) the rules are:
In no case do three or fewer points trigger an out of control alarm until you get beyond 2σ.
Three points define a plane to a mathematician, or a line to an engineer, but don't quite suffice for a trend under Western Electric control chart rules.
That being said, I start to watch a process very closely when three consecutive points are on the same area...