  Robots are being designed to communicate with people in various public and
domestic venues in a helpful, discreet way. Here, we use a speculative approach
to shine light on a new concept of robot steganography (RS), that a robot could
seek to help vulnerable populations by discreetly warning of potential threats.
We first identify some potentially useful scenarios for RS related to safety
and security -- concerns that are estimated to cost the world trillions of
dollars each year -- with a focus on two kinds of robots, an autonomous vehicle
(AV) and a socially assistive humanoid robot (SAR). Next, we propose that
existing, powerful, computer-based steganography (CS) approaches can be adopted
with little effort in new contexts (SARs), while also pointing out potential
benefits of human-like steganography (HS): although less efficient and robust
than CS, HS represents a currently-unused form of RS that could also be used to
avoid requiring computers or detection by more technically advanced
adversaries. This analysis also introduces some unique challenges of RS that
arise from message generation, indirect perception, and effects of perspective.
For this, we explore some related theoretical and practical concerns for
selecting carrier signals and generating messages, also making available some
code and a video demo. Finally, we report on checking the current feasibility
of the RS concept via a simplified user study, confirming that messages can be
hidden in a robot's behaviors. The immediate implication is that RS could help
to improve people's lives and mitigate some costly problems -- suggesting the
usefulness of further discussion, ideation, and consideration by designers.
