Comparison of the proper motion distribution between the BHB–BS S3 training sample from N19 (orange circles) and the newly identified S3 candidates (beige and red transparent circles), overlaid on the Gaia DR3 sample (background histogram; see Sect. 2.2). The dashed black and white line indicates the polygon selection applied in proper motion space (see Sect. 3.1). The newly identified S3 candidates are shown in beige if they lie inside the polygon selection, and in transparent red if they fall outside it. The cyan and magenta crosses indicate the systemic motions of the LMC and SMC, respectively. In the background, regions of higher (lower) density are shown in bluer (redder) colour.