The United States Postal Service has no official creed or motto. An inscription on the James Farley Post Office in New York City reads:

Neither snow nor rain nor heat nor gloom of night stays these couriers from the swift completion of their appointed rounds.

This phrase was a translation by Prof. George Herbert Palmer, Harvard University, from an ancient Greek work of Herodotus describing the Persian system of mounted postal carriers c. 500 B.C.E. The inscription was added to the building by William Mitchell Kendall of the architectural firm of McKim, Mead and White, the building's architects. It derives from a quote from Herodotus' Histories, referring to the courier service of the ancient Persian Empire:

It is said that as many days as there are in the whole journey, so many are the men and horses that stand along the road, each horse and man at the interval of a day's journey; and these are stayed neither by snow nor rain nor heat nor darkness from accomplishing their appointed course with all speed. - Herodotus, Histories (8.98) (trans. A.D. Godley, 1924)

In Adventures in Odyssey, the character Wooton Bassett said the mailman's motto is:

Rain or shine, snow or sleet, we deliver your mail! (But sunny days are optional...)