Who can sign as incorporator on California form ARTS-GS?

Ordinarily it wouldn't matter too much who signs as incorporator, as that person needs not be an intended shareholder, officer, director, etc. (though if using the ARTS-GS form, it should be someone who you trust enough to resign as incorporator and appoint the initial directors, or else there could be issues). But in this instance, since your brother reserved the corporate name, he should be the one to sign as incorporator. Delays are almost certain if name of the person who reserved the corporate name and that of the incorporator do not match. Best of luck.

Mr. Doland and Mr. Pham are right on with their responses. The "Incorporator" is not necessarily and not typically someone that will be involved in the corporation once it is organized, and an organizing attorney frequently signs as incorporator and resigns at the first meeting. If you sign, you can do so as attorney in fact (with a power of attorney) or as the incorporator and then resign after adopting by laws and appointing an initial board of directors to complete the organization and set up. I'd recommend contacting an attorney locally to assist you, so that the organization is complete. Good luck.