I have noticed that my speedo has a light for neutral and another position for a second light.

Anyone know if this should be another indcator?  Should it be illuminated?

Has anyone ever attempted to rig a low fuel lamp to that position?

No smiley face ?????

To do that (low level warning) you need a sensor.
If you're gonna put in a sensor, why not a level gauge?

A cheap sight gage would be a tee junction and piece of hose off the rubber exit tube at the bottom of the petcock leading to a permeable capped small diameter glass tube that the top cap happened to only slightly taller than the gas height in the gas tank.

Such need not even be attached to the tank (where you couldn't see it when riding) but it could be attached to the fork tube/triple tree where you could see it while riding.   I'm thinking lab glass here, hard to break.

A good, steel wrapped piece of "motion wear proof" hose, such as the hose they sell for hydraulic uses would be good here, because if it leaks it could empty your tank and strand you, or even catch your bike on fire.

This would double as an evaporation gage for your bowl as the glass tube would go clear before the bowl went empty.

Glass tube mounted on the triple tree would also be easy to replace if the glass tube got clouded by evaporation products (it will happen).

Failure mode for such a system would be busting the glass by accident -- put a cut off in the system on the run up from the petcock for such accidental events would be wise.

Simplest solution is: buy yourself a grease pencil ( retractable ones are a buck, and are available at craft stores, art supply stores, or millenaries). When you fill up write the mileage +100 on the mirror with the grease pencil (also called a china marker). When the mileage on the odometer starts getting close to the mileage you have written on the mirror, get gas. Easy peasy Japaneasy.
I haven't had to put it on reserve since I started doing this.