No signal velocity can exceed the speed of a light pulse in a vacuum (by special relativity).
However, in a few special cases (e.g., media designed to amplify the front-most parts of a pulse and then attenuate the back section of the pulse), group velocity can exceed the speed of light in vacuum, while the signal velocity will still be less than or equal to the speed of light in vacuum.
In electronic circuits, signal velocity is one member of a group of five closely related parameters.
In these circuits, signals are usually treated as operating in TEM (Transverse ElectroMagnetic) mode.
In a transmission line, signal velocity is the reciprocal of the square root of the capacitance-inductance product, where inductance and capacitance are typically expressed as per-unit length.
In circuit boards made of FR-4 material, the signal velocity is typically about six inches (15 cm) per nanosecond, or 6.562 ps/mm.
In circuit boards made of Polyimide material, the signal velocity is typically about 16.3 cm per nanosecond or 6.146 ps/mm.