For many parts of the world, you will not only have to sign a document in front of a notary, but also have it legalised.
Legalisation is required in Europe, some states in the USA and most other parts of the world. In most cases an apostille is all you need to satisfy the legal requirements.
An apostille is a certificate issued by the Foreign & Commonwealth Office confirming that I am a notary.
In some cases documents have to be legalised at the embassy or consulate of the relevant country as well as being apostilled.
Legalisation is not required in most Commonwealth countries.