| 摘要 |
A signal device consisting of first and second inks applied to a surface. The first ink is sensitive to either light or air. The second ink is stable in the presence of light and/or air. The surface having first and second areas, wherein the second ink is applied in work or character form to said first area to form a signal word. The first ink is applied to the second area and is of a color so as to cooperate with the second ink to camouflage the signal word. A protective shield blocks the sensitive ink from exposure to light and/or air, wherein after a metered period of time of exposure to light or air the sensitive ink fades such that the contrast in color between the faded sensitive ink and the stable ink reveals the signal word.
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