Panel a: distribution in proper-motion plane of all Gaia sources falling in the cluster region defined in Fig. 6, and having errors on μ_α and μ_δ less than 0.5 mas yr⁻¹. The dotted contours describe instead the proper-motion distribution of Gaia sources in the reference region defined in Fig. 6, excluding those in the cluster region. Panel b: map of density difference between Gaia sources in cluster and reference regions, scaled by respective total sources numbers, in proper-motion plane. Red dots are NGC 6530 X-ray sources. The blue rectangle indicate the cluster boundaries in the proper-motion plane. Contours are the same as in panel a. Panel c: map of density difference between Gaia sources in cluster and reference regions, scaled by respective total sources numbers, in μ_α-parallax (π) plane. The maximum parallax error for inclusion is 0.3 mas. Red dots are NGC 6530 X-ray sources. Black dots are candidate M giants. The blue rectangle indicate the cluster boundaries in the μ_α-parallax plane. Contours describe the distribution of sources in the reference region. Panel d: wider-scale view of the μ_α − π plane of panel c. The green rectangle is the same as the blue rectangle in panel c. Black (blue) dots indicate low-reddening M stars in the cluster (reference) region, while red (orange) dots indicate CTTSs in the cluster (reference) region.