。
Be kind to old people.
Literal
Old-people [to-に] kind do [soft imperative-なさい].
親切にする ('to be kind to') uses the na-adjective 親切 adverbially with the auxiliary する. ~なさい marks this as an instruction from authority — a parent or teacher addressing a child. The directive carries cultural weight, reflecting the deference Japanese society places on respect for elders.