What about "503: Service Intentionally Unavailable"?
Edit: Actually, I don't want to change it. I don't think our readers will read three words and skip the explanation. I think much more highly of them than that.
The thing is, people are trained to skip error pages. What do you think would happen if you format it as parked domain page? It's not the users you'd perhaps think lowly of that have the most trained impulse to close error pages; it's the more technical users.