Sprinkle 2 tablespoons Tajin seasoning evenly in the bottom of 2 ice cube trays (16 ice cubes). Fill with water and freeze.
In a saucepan, stir together 1 cup sugar and 1 cup water over medium-high heat. Bring to a boil, stirring frequently, until sugar dissolves. Remove from heat and let cool until room temperature.
In a large pitcher or bowl, stir together lime juice, sugar mixture and remaining 3 cups water. On a small plate, combine remaining 1 tablespoon Tajin seasoning and 1 tablespoon sugar. Moisten rim of 8 tall glasses with lime wedges; dip rims in Tajin mixture. Place 3-4 ice cubes in each glass; fill with limeade. Garnish with lime wedges if desired.