Template:Unsigned

—The preceding unsigned comment was made by User: (talk • contribs).

Documentation
If you see an unsigned comment on a talk page (or anywhere else where edits should be signed with ), it is generally good practice to check the page's edit history to determine who made the comment, and when.

Once you have that information, you can then append this template to the end of their comment. The template takes two unnamed parameters: the username of the user, and an optional second parameter that allows you to append additional information like the date and time of the edit.