The kings Fernando and Isabel gave the city in 1508 her own coat of arms (seal).
"A la Villa de Santo Domingo se?alo e doy por armas un escudo en que est?n dos leones dorados, tiene en lo alto una corona de oro, entre ambos leones, en medio de ellos una llave azul en campo colorado en derredor circulando al escudo con una cruz blanca e prieta en el mismo campo del bienaventurado se?or Santo Domingo."
The above is the proclamation of such notice by the King to the City.
It says that the Villa of Santo Domingo was to receive the seal and coat of arms including the exact elements that conforms it.
The crown means that the villa is "Realenga" a royal city under the auspices of the crown and not any other potentate or sireship.
The Lions are the representation of the armies of Castilla and Leon, side by side facing the key of the city. The colors that surround the seal are in fact a cross just like the "Baculo" carried by Santo Domingo de Guzman (the saint) and incorporated into the seal. The black and white represent purity and atonement, death and resurrection. The key represents the fidelity and relation to the royal crown.
The crown atop the seal and within the seal has two meanings:
The one above it gives it the royal authority over the villa and the one in the seal constitutes the consolidation of the royal crown over the city as "royal villa".