Help:Signature
From Xiandos Info
[edit] How To Sign Your Discussion Entry
Some users, particularly ones that haven't registered and thus obtained a user name, omit signing their talk page submissions. In order for all users to see when an entry was posted and also to be able to see all entries from a user (or IP), it is recommended that that you use the standard procedure for signing a discussion entry.
An automatic signature is generated when you end your post with ~~~~ (four tildes). Please do that whether or not you have registered an account. It makes it easier to follow discussions!
P.S. There is also a button above the edit window which performs this function.