Some identifiers are permanent for a ship while others may be changed at the owners' discretion although regulatory agencies will need to approve the change. Modern ships usually have several identifiers.

In addition to proper nouns, types of ship identifiers include:
*Code letters - an identifier for a ship that is displayed on vessels by ICS flags representing the letters of the alphabet and numbers 0-9, e.g. the flags (from top to bottom) represented the identifier "USMW"
*Hull number