Google says:    Box 2e - Section 897 ordinary dividends: Shows the portion of the amount in Box 1a that is section 897 gain attributable to disposition of U.S. real property interests (USRPIs).

You enter this on the bottom of the Additional Information Dividend Income Worksheet  in Section F just below Foreign Tax information

It also says that in the Instructions for Recipients of Form 1099 that most people get with their 1099s.