From the Model Mayhem FAQ:

What is an availability or travel notice?
Notices are alerts to other members that you are available to work. There are two different classifications of notices:

- Availability notices are local to your home region and let others in the same area know you are ready to work.
- Travel notices are specific to a place you will be going to in the future, and let people in that area know you will be coming and are ready to work.