Security symbols printed on a substrate

A substrate having a front side and a back side and being printed with front side markings on the front side and back side markings on the back side,

• the front side having front side markings, the front side when viewed with reflected light comprising:
• a first marking printed with a first gradient of two colors, the first gradient flowing from a first color, to a second color, back to the first color;
• and
• a first symbol printed with a third gradient of two colors, the third gradient flowing from a fourth color, to a fifth color, back to the fourth color;
• the back side having back side markings, the back side when viewed with reflected light comprising:
• a third marking printed with a fourth gradient of two colors, the fourth gradient flowing from the fifth color, to a sixth color, back to the fifth color;
• a fifth symbol printed with a second gradient of two colors, the second gradient flowing from a third color, to the first color, back to the third color;
• and
• the first color, the second color, the third color, the fourth color, the fifth color, and the sixth color being selected, when viewed from the front side with transmitted light, to be subtractive between the front side and the back side, to show all symbols and markings in black color by incorporating complementary colors between the front side and the back side.

A substrate having a front side and a back side and being printed with front side markings on the front side and back side markings on the back side,

• the front side having front side markings, the front side when viewed with reflected light comprising:
• a first marking printed with a first gradient of two colors, the first gradient flowing from a first color, to a second color, back to the first color;
• and
• a first symbol printed with a third gradient of two colors, the third gradient flowing from a fourth color, to a fifth color, back to the fourth color;
• and
• the back side having back side markings, the back side when viewed with reflected light comprising:
• a third marking printed with a fourth gradient of two colors, the fourth gradient flowing from the fifth color, to a sixth color, back to the fifth color;
• and
• a fifth symbol printed with a second gradient of two colors, the second gradient flowing from a third color, to the first color, back to the third color;
• the first color, the second color, the third color, the fourth color, the fifth color, and the sixth color being selected, when viewed from the front side with transmitted light, to be subtractive between the front side and the back side, to show all symbols and markings in black color by incorporating complementary colors between the front side and the back side.