We introduce a steganographic information hiding scheme based on structural properties of numerical semigroups arising from the Frobenius coin problem. Instead of encoding data through representable integers, the proposed protocol embeds information into the gap structure of carefully chosen symmetric numerical semigroups. Symmetry guarantees a balanced gap density, ensuring that encoded values are statistically indistinguishable from uniform numerical noise to an observer lacking the private generating set. The security of the scheme relies on the assumed average-case hardness of numerical semigroup membership inference for hidden generators, offering a novel number-theoretic primitive for covert communication and post-quantum resilient information hiding.