In the late 80s/early 90s, Japanese car modders used to hang mini videogame character figures on a piece of string from the rear view mirror to see how near the limit of traction they were getting when drifting. The bike indicator wouldn't need to measure an exact angle of lean, it would only need to display something as a relative marker. e.g. when my knee's on the floor, the marker is in this position.
As johnv writes, any accelerometer based angle sensing device will give you an accurate static readout, but is no good for dynamic testing, as the bike leans proportional to the corner speed, the accelerometer is unable to detect that you've leant at all. i would suggest that some work on body position whilst cornering would be more useful? I used to ride fast on the road, and had no chicken strips. Then I went racing, and quickly learned to increase corner speed beyond what was possible before by hanging off the bike in corners and transferring my body weight inside the bike, keeping the bike as upright as possible. I ended up faster, and with chicken strips again, now I have chicken strips always, which I see as safety margin so I'm happy...
Just to point out that any gizmo that measures lean angle needs to be based on a gyroscope (or electronic equivalent) if you're going to use it on a moving bike. Anything that measures based on acceleration (including that mechanical dial gauge finder shown above) will be affected by the very forces that allow the bike to lean over. Since the iPhone 4, the iPhone has included a gyroscope as well as accelerometers, so that it can detect true lean angle.
Is that right Snips? Very interesting, I have an interest in gyro stabilised accelerometer sensors, I had no idea I have been carrying one around in my pocket!!
