You can set boolean prop to false from markup by 0 or false string

define('my-element', class extends WeElement {
  static defaultProps = {
    show: true
  }

 static propTypes = {
    show: Boolean
  }

  render(props) {
    ...
    ...
  }
})

Use:

<my-element show="false"></my-element>

or

<my-element show="0"></my-element>