All forms should ideally have a “multiracial” box to check.
As an alternative, you may use the check all that apply format and put this wording in the instructions:
If you are multiracial, you may select two or more races.
Project RACE never requires a membership fee. We are a non-profit, 501(c)(3), all volunteer organization supported by individual donations, contributions and grants. Donations are deductible, as provided by law. If you believe in our cause, please consider making a difference for multiracial people.
Being a part of an established community conquering racial identity makes multiracial people a part of a true movement. You can feel accepted and understood. You can pass our work on to your family and educate friends and the establishment. You can join us and do as much or as little as you please. Won’t you join us?