System for and method of producing a security mark on a micro-porous stucture

A system for producing a security mark on a micro-porous structure to be secured, comprising:

• means for forming selected portions of the micro-porous structure in a pattern corresponding to the security mark to be produced;
• and
• means for changing light transmission characteristics of the selected portions to transmit light through the selected portions at different light levels to render the security mark visible when the micro-porous structure is illuminated.

A secured document, comprising:

• a micro-porous structure configured as a polymeric sheet having opposite major surfaces and containing a multitude of pores that constitutes at least 50 percent by volume of the micro-porous structure,
• selected portions of the micro-porous structure being arranged in a pattern corresponding to a security mark to secure the document, and
• the selected portions having changed light transmission characteristics to transmit light through the selected portions at different light levels to render the security mark visible when the micro-porous structure is illuminated from at least one of the major surfaces.