Reference
Postmarks and cancels
A postmark is the strongest evidence a postcard can carry: it records a real date, on a real day, at a named post office. When the dial is crisp you are done — no decoder needed. This page is about the other case, when the date is smudged, clipped or half-struck, and the type of marking has to do the work instead.
Read the dial first
The circular dial carries the office and the date. Even a partial strike often yields a year, or the last two digits of one. A postmark dates the mailing, not the printing: a card can be years old by the time someone writes on it, so a postmark is a latest-possible date for the card’s production, not the production date itself.
When the date is gone, the marking type still helps
Machine cancels with advertising or public-service slogans belong to particular campaigns, so the wording itself carries a rough period. Flag cancels, duplex handstamps and railway post office marks each belong to broad eras of postal practice. None of these is as precise as a legible dial, and we would rather give you a decade you can trust than a year we invented.
HIRE THE HANDICAPPED — IT’S GOOD BUSINESS
slogan cancel · campaign from 1945–46; slogan cancels documented from at least 1949

The wording comes from the federal National Employ the Physically Handicapped Week campaign, established by act of Congress and presidential proclamation; a campaign poster with this slogan was issued for the week of 6–12 October 1946.
Government programme guides using the same slogan were published for the campaign weeks of 1948 and 1953, and related material continued into the 1960s.
Machine slogan cancels with this wording are documented on mail from at least January 1949 (Boston) and 1952 (Rochester, New York).
What it does and doesn’t tell you. We have not found a documented first and last day for this slogan die, so treat it as a broad mid-century indicator — roughly the late 1940s onward — rather than a narrow date range. The dial beside the slogan carries the actual date; read that first.
Sources: National Employ the Physically Handicapped Week campaign materials, 1946, 1948 and 1953: US Government Monthly Catalog records; Documented slogan-cancel uses: Smithsonian Institution transcription of a 1949 Boston postcard; philatelic listing of a 1952 Rochester, N.Y. cover
Pair a postmark with the stamp above it and the rate it paid: together they usually bracket a card tightly, even when no single clue is decisive.