Immigration stamps in passports

For immigration control, immigration officials of many countries stamp passports with entry stamps and exit stamps. A stamp can serve different purposes. In the United Kingdom, an immigration stamp in a passport includes the formal leave to enter granted to a person subject to entry control. Otherwise, a stamp activates or acknowledges the continuing leave conferred in the passport bearer’s entry clearance.

Under the Schengen system, a foreign passport is stamped with a date stamp which does not indicate any duration of stay. This stamp is taken to mean either that the person is deemed to have permission to remain for three months or for the period shown on his visa.

Neither the UK nor a Schengen country is allowed to stamp the passport of a person not subject to immigration control, whether a citizen of that country or a national of another EU country. Stamping is prohibited, because a passport stamp is imposition of a control that the person is not subject to. This concept is not applicable in other countries, where a stamp in a passport simply acknowledges the entry or exit of a person.

Countries have different styles of stamps for entries and exits, to make it easy to identify the movements of persons. The colour of the ink may also provide information about movements. In Hong Kong, prior to and immediately after the 1997 transfer of sovereignty, entry and exit stamps were identical at all ports of entry, but colours differed. Airport stamps used black ink, land stamps used red ink, and sea stamps used purple ink. In Macau, under Portuguese administration, the same colour of ink was used for all stamps. The stamps had slightly-different borders to indicate entry and exit by air, land, or sea. In several countries the stamps or its colour are different if the person arrived in a car in opposite to bus/boat/train/air passenger.

source : http://en.wikipedia.org/wiki/Passport