By John L. Mone and Will Weissert, Associated Press HOUSTON — At Tacos Tierra Caliente — a food truck parked in a section of Houston where Spanish is spoken as often as English — $1.50 can buy such street taco staples as pollo (chicken), barbacoa (shredded beef) and lengua (tongue). But next to the handwritten chalkboard menu and “cash only” sign is a new red, white and blue placard that commands: “Registrarse y Votar” (Register and Vote).