By using a new materials system, we developed invisible passive infrared markers that can take on various visual foreground patterns and colors, including white. The material can be coated over many different surfaces such as paper, plastic, wood, metal, and others. Dual-purpose signs are demonstrated where the visual foreground is for human view while the infrared background is for machine view. By hiding digital information in the infrared spectral range, we can enable fiducial markers to enter public spaces without introducing any intrusive visual features for humans. These fiducial markers are robust and easy to detect using off-the-shelf near infrared cameras to assist robot positioning and object identification. This can reduce the barrier for low-cost robots, that are currently deployed in warehouses and factories, to enter offices, stores, and other public spaces and to work alongside with people.