The cross certification form is here.

As the form says, you must get it signed by the USSF state referee administrator. The state administrator for our state association, "California North," is 

 

After you get the USSF signature, you must do the following:

1. Complete and submit an AYSO volunteer application form (required annually). See this link, http://www.davisayso.org/training.htm, for how to do it.
2. Take the AYSO Safe Haven online course at www.aysotraining.org. To do so, you must first submit the volunteer application form; after it is submitted, you will get an AYSO ID number. The number is required in order to take and get credit for the course.
3. Finally, get the signature of the Davis AYSO Regional Commissioner (commissioner@davisayso.net). Send the form to the AYSO National Office; see this page for the address. The AYSO National Office will send you a badge.