From Robert Zimmerman’s web site Behind the Black on July 8, 2019.
Sunspot update June 2019: Down to zero again, with next cycle making an appearance
“How do we know this sunspot belongs to Solar Cycle 25? Its magnetic polarity tells us so. Southern sunspots from old Solar Cycle 24 have a -/+ polarity. This sunspot is the opposite: +/-. According to Hales Law, sunspots switch polarities from one solar cycle to the next. AR2744 is therefore a member of Solar Cycle 25. “