Comparison of a solar and a model spectral line bisector. Left: solar Fe I line at 5003.25 Å (solid black) with its center marked by a vertical line (solid black) from the IAG solar flux atlas (used as a template in this work) and the corresponding line bisector (dashed red). Right: Gaussian model line profile without (solid black) and with a solar-like third signature (dashed red, following Eq. (1)). Their respective bisectors are shown in the same colors. The model with the signature is shifted to match the line cores. In both panels, to emphasize the slight blueshift, the bisector scale is amplified by a factor of ten.