I don't understand what the robotic arm has to do with a watch.
If the device you're wanting to build is sized like a watch, then all you need is a small, flat, stepper motor, and a suitable battery and control circuitry. I don't know if you can get these off-the-shelf, but you can get them made. Battery life will be a problem.
Would you consider an electronic display? New "smart watches" like Pebble or Galaxy Gear allow you to display your indicator in software, which is much easier to work with and prototype :-)
Finally: Post your drawings! Nobody will understand your concept unless you do, and thus all advice you get will be poorly matched to the idea. In the start-up world (Silicon Valley, etc,) it's very common to release early (way before anythings "ready" or "good") and use all the feedback to improve the concept and design. It turns out, what you end up with is a much better fit to the market needs than what you'd get if you just used yourself as the only source of input until the end.