Yup, revision symbol. It was standard with some companies to reduce drawing clutter by scrubbing rev symbols IF the revision was incorporated in a subsequent release. Others preferred leaving them as history, in addition to the ECN.
Point: One thing people forget is whether the light available out in the shop is enough to avoid confusion when you start playing with colors on a print. Blue, black, red, yellow and green lines, representing different values and details can easily be confused when the lighting is dim.
Point...
