Signal Sticks are 1/4 wavelength on the primary frequency (2 meters); they handle 70cm by a convenience of math that says that a 1/4 wavelength on 146MHz is also a 3/4 wavelength on 440MHz.

In order to work on 6 meters it would need to be a 1/4 wavelength on 6 meters. A 6 meter signal stick would be about 51 inches long; we’ve been experimenting with making longer Signal Stalks (vehicle mount) and a 40" long Signal Stalk is only barely usable – and only because we use 3mm diameter wire for it. Signal Sticks are made with 1.5mm diameter wire. In short, a 6m signal stick would be too long to even stand up on its own.