SPLIT= identifies the asterisk as the character that starts a new line in column headers. The N option prints the number of observations at the end of the report. OBS= specifies the column header for the column that identifies each observation by number. The split character (*) starts a new line in the column heading. Therefore, the equal signs (=) in the value of OBS= underline the column header.
proc print data=exprev split='*' n obs='Observation*Number*===========';