If you come across an unsigned comment on a Talk page, feel free to browse the page history and determine who added that comment to the page, then use the {{unsigned}} template, like so:
{{unsigned|ianweller}}
if Ian Weller is the person who did not sign his comment. Then, kindly remind the user to sign their comments by placing the following message on their user talk page:
You recently added a comment on [[Some random page]] which you did not sign; I have signed it for you. Please remember sign all comments on talk pages with <code><nowiki>--~~~~</nowiki></code>, or by pressing the signature button in the button bar above the edit box. This will be replaced with a link to your wiki page and a timestamp. Thanks --~~~~
Be sure to replace the "Some random page" link.