It shouldn’t need to be be policed by looking in people’s pants. Everyone knows what sex they are, it is up to individuals to follow the law, not for the public to enforce it.
On a motorway, if someone decides to travel at 90mph, it’s not up to the surrounding drivers to TPAC the offender and surround his car, forcing him to slow down and obey the law. It’s up to the individual to comply of his own accord.