Top panel: distribution of Swift/BAT S/N values of 1000 random blank sky positions. The red line indicates a Gaussian fit with center of 0σ and width 1σ. The red shaded region indicates 3σ uncertainty ranges for the norm of the fitted function. Middle panel: distribution of Swift/BAT S/N values of the MOJAVE-1 sample. The red line indicates a Gaussian fit with center of 0σ and width 1σ to the distribution with values smaller than 0σ. The red shaded region indicates 3σ error ranges. The 4.8σ threshold of the 105-month BAT survey is shown by the dashed line. Bottom panel: resulting histogram after subtracting the MOJAVE-1 S/N distribution by the distribution described by the Gaussian fit. Arrows indicate the cutoff at 15σ (for better readability).