These digits are often used with a decimal separator which indicates the start of a fractional part , and with one of the sign symbols + ( positive ) or â ' ( negative ) in front of the numerals to indicate sign . These digits are often used with a decimal separator which indicates the start of a fractional part , and with a symbol such as the plus sign + ( for positive ) or minus sign â ' ( for negative ) adjacent to the numeral to indicate whether it is greater or less than zero , respectively .