Shield: From the Provincial Seal of Isabela where the town is located.
Sun in Triangle: Emphasizes the importance of sunshine to the town's agricultural industry.
Green Triangle: Color: Growth which also suggests that the town is an agricultural community. Shape: Three (3) important factors in agriculture -- man, land and water.
Letter "T": "Tomas", name of the two (2) prominent pioneers of the town: Tomas Gatan and Tomas Bautista, after whom Santo Tomas was named.