Security articles comprising groups of microstructures made by end milling

An article, comprising:

• a substrate having a structured surface that extends along a reference plane, the structured surface including cube corner elements formed therein;
• wherein the cube corner elements comprise first cube corner elements and second cube corner elements that differ from each other to define indicia;
• and
• wherein at least some of the cube corner elements each have a compound face that includes a first face and a second face that meet along a break line, the break line being inclined relative to the reference plane.

A method of making a security article, comprising:

• providing a substrate having a working surface, the working surface extending along a reference plane;
• and
• forming a plurality of microstructures in the substrate, the microstructures including first microstructures and second microstructures that differ from each other to define indicia;
• wherein the forming includes:
• cutting the substrate with a rotating end mill to form a recess in the substrate;
• and
• during the cutting, causing the rotating end mill to move along a cutting path relative to the substrate, wherein the cutting path includes a path portion that is inclined relative to the reference plane.