Redline, it's a cautionary symbol for an approach to a "point of no return". Whether its the reading on a tachometer in some high performance vehicle indicating its engine's RPM's is reaching a point that could destroy the engine or some sensed line that just is too dangerous to cross. We encounter these in many various instances and need to acknolwlegde their existence and make decisions regarding them. These drawings are the physical manifestations of some of my museings about this subject.