Dear Student,
Answer to your question is as follows :
Most of the Ashoka's inscription were in Prakrit and were written in the Brahmi script, so as dhamma.
Dhamma is also a Prakrit word for the sanskrit term ' Dharma'.
To spread Dhamma's message
He appointed officials, who known as the dhamma mahamatta who used to went from place to place to teach people about dhamma.
Ashoka got his messages inscribed on rock and pillars as well and even asked his officials to read such message to ones who could not read it by themselves.
He also sent messengers to other lands such as Greece, Egypt etc to spread ideas about dhamma.
Regards