Updated Documentation: The Online Manual has moved. All updates to the documentation are now taking place in the new Online Manual. Please see the new Online Manual, and learn how you can help, as it continues to grow and improve.
Signatures are a part of a Member's profile, which are usually displayed beneath a post made by that user in most themes. When the member changes the signature in their profile, it will be changed for all of the posts they have made automatically.
Signatures can be formatted much like posts, although it is generally considered to be rude to have a very large or very flashy signature. Rules about this vary from forum to forum. The maximum length of signatures is changeable in the administrative settings. By default, this cannot be larger than 65,535.