For sddm edit <b>/usr/share/sddm/themes/breeze/clock.qml</b> and adding an extra label entry after the last one:

```
Label {
        text: "Property of ****** - If found call **********"
        font.Bold: true
        font.pointSize: 16
        Layout.alignment: Qt.AlignHCenter
}
```
For lock screen change <b>/usr/share/plasma/look-and-feel/org.kde.breeze.desktop/contents/components/clock.qml</b>