Apostille is a French word meaning "certification." An Apostille seal does not mean the stamp or seal of a notary public stamp. In USA, apostille seals are administered only from the secretary of state's notary public. In Hong Kong, the apostille seal is affixed by the High Court of Hong Kong.
Apostille seals were introduced to the 1961 Hague Convention Abolishing the Requirement of Legalisation for Foreign Public Documents. The convention established rules governing the international recognition of legal documents. Not all countries are its treaty members.
Notarial or legalization importance of an apostille seal
An Apostille seal means the document can be used legally in a foreign country. However, only countries that signed Article 12 of the 1961 Hague convention will honour an Apostille. The rest or non-member states or countries may require legalization by the emabssy or consulate-general.
In Hong Kong, not all documents may be submitted for an apostille. A document signed by a notary public is one of the two types of documents qualified to be apostilled. See Documents acceptable for apostille in Hong Kong