Using a "Do Not Disturb" sign can be as effective as not answering the phone as long as the people around you heed it. The idea here is again that interruptions take up precious time. If your time is valuable enough; it will be worth it to not be disturbed during certain activities.
I use a "Do Not Disturb" sign when I am with my one-on-one clients so that people around my office know not to barge in (although my sign does not look like the one pictured to the right).
This concept of a "Do Not Disturb" sign is especially important with home based businesses where family tends to just walk in. This can be a hindrance to your productivity.
We have uploaded a special Time Managed "DO NOT DISTURB" sign that you can print and utilize HERE.