Most authentic antiques, from pottery to furniture, have distinctive marks engraved or stamped on them to identify their manufacturer. These marks are used today to help appraisers determine the time period in which an antique rocking chair was crafted and by whom. Unfortunately, it's only possible to date and identify furniture from the 18th century and later because it wasn't until this time period that the practice of marking a piece with a distinctive company symbol became more common among furniture craftsmen. Therefore, it is more difficult to locate a manufacturer's mark on pieces that were made earlier, and thus, harder to authenticate.
Determine what style of rocking chair you own. Some of these would include Colonial, Louis XIV, XV, or XVI, Chippendale and Art Nouveau among many others. The style is important since many manufacturers and designers were best known for crafting only one style. So if a designer was popular for a Regency, it is most likely that he would not build a Jugendstil style of rocking chair.
Locate the manufacturer's mark. They can be found in different forms, including as a label that has been pasted on with information written in pencil or ink, branded on with a hot iron or stamped on with a steel die. Certain practices are attributed to specific regions and nationalities of the world and may also help in tracing a chair's origin. In almost every instance, the mark will be found on the underside of the seat with as much information as was the norm at the time of manufacture.
Consult an appraiser with the label or stamp found underneath the chair. Take a photograph of the mark and scan or fax it to an expert. Many of them have reference books cataloging all of the marks of antique furniture makers throughout history. There are also some sources on the Internet that can be found, although in many cases, their references may be incomplete.
Beware of forged manufacturer's marks, particularly those that are labels. Some people have tried to pass off old newspaper advertisements or old letterhead as authentic labels. These can be determined as forgeries by looking for simple things like label borders and typography font or even moistening the label to remove it and check for any visible writing on the back.