2013 California Standards for Accessible Design Pocket Guide

11B-411.2.1.2.1 Keypads.

Keypads shall be in a 12-key ascending telephone keypad layout. Characters and symbols shall be centered on the corresponding button. The number five key shall have a single raised dot. The dot shall have a base diameter of  0.118 inch (3 mm) minimum and 0.120 inch (3.05 mm) maximum and a height of 0.025 inch (0.6 mm) minimum and 0.037 inch (0.9 mm) maximum. Keypads shall have a star (*) on the lower left button and a minus sign (-) on the lower right button.  From any level above and below the main egress level, when the star button is pressed an elevator shall be dispatched to the main egress level.