@Stephen Marsh thanks for the shoutout.
For a simple "working on it" message, this is what I use...
// CREATE WORKING WINDOW
var working = new Window("palette");
working.preferredSize = [300, 80];
working.add("statictext");
working.t = working.add("statictext");
working.add("statictext");
working.display = function (message) {
this.t.text = message || "Working... Please wait...";
this.show();
app.refresh();
};
// USAGE
working.display();
// Gives the default message. Want something else? Pass it.
working.display("A different message");
// When done...
working.close();
// It is also possible to .hide() and .show the window.
working.hide(); // It goes away but still exists.
working.show(); // Now it is back.