(additional suggestions from Paul Wisner below)

Required parts / pieces / etc
1) Sigma BC800
2) Small button magnet (1/2" or less - from Home Depot / Lowes / Radio Shack)
3) Quick set epoxy
4) Miniature wire ties
5) Depending on mounting location, you may also want to get the rear wheel mounting kit. Normally offered so that the Sigma can be mounted to the rear wheel of a bicycle, but for the motorcycle, it gives more cable length and thus more choices of mounting locations.
 
** Important Note: Passed on by Neil Anderson - When purchasing a button magnet, be sure that it is magnetic on both sides (check by attaching it to metal on both sides) - Neil got one that was magnetic on one side only (had North and Soth poles on one side) and it failed to activate the Sigma sensor.
 

1) Begin by mounting the button magnet on the carrier of the right front disk (using the epoxy). You'll want to mount it in such a way that it will pass close to the sensor on each revolution.
2) Mount the Sigma sensor on the lower front edge of the right caliper using two small wire ties. For added security, you may want to add a drop of epoxy between the sensor and the caliper. When mounting, pass the magnet by, to make sure they are aligned and that they don't make contact.
3) Using the miniature wire ties, run the sensor wire along the speedo cable, using a wire tie every few inches. If you position the sensor cable behind the speedo cable, it will not be visible to the casual observer.
4) Run the sensor wire up to your desired mounting location, remembering to leave enough slack for bars turning and fork extension.
5) Mount the Sigma bracket in a location that will be easy to view.
 
That's all there is to it - piece of cake !
 
One note: When setting tire size, with a stock tire, use 1164 for mph or 1874 for kmh

(from Paul Wisner)

I mounted a BC1200 on my ST over the weekend and discovered that is was simpler to do than indicated.

1) The standard magnet supplied with the BC800/1200 is fine and will work on the ST. I have included pictures of the installation which makes it easy to see. I experimented on the bench with magnet orientation to the switch and found that it is not sensitive to orientation (just distance). Seems to work better if the magnet is passed closer to the tip of the receiver switch (away from the wire end).

2) Small plastic ties are all that is necessary to mount. Epoxy wasn't needed on mine. The small groove of the magnet should be placed on the edge of the carrier to get is closer to the pickup. Mine as shown in the picture is 4mm clearance.

3) The standard length pickup wire was too short to go from right caliper to left handle bar. I used the longer "rear wheel" version so that I didn't have to cut and splice any wires.