Schematic illustration of the polarization from synchrotron emission from a random magnetic field. Left: illustration of the emission of the photons toward an observer with a line of sight forming a viewing angle θ_v with the jet. The emission stems from magnetic field lines with a randomized direction within the ejection plane, that are indicated with the purple line. Middle: the observer sees the emission area with a size of 1/Γ (shown in gray) within the jet (shown in purple). The polarization vectors of the photons are indicated as black arrows with the direction indicating the polarization angle and the size representing the PD. For an observation area contained within the jet, the PD is 0% due to canceling out of the polarization vectors within this area. Right: as in the middle panel, in a situation in which the observed area is not fully contained in the jet, allowing for a net observed polarization, with a polarization angle aligned to the off-axis viewing angle ( θ_υ = ι).