A racemic mixture is denoted by the prefix (±)- or dl- (for sugars the prefix - may be used), indicating an equal (1:1) mixture of dextro and levo isomers. Also the prefix rac- (or racem-) or the symbols RS and SR (all in italic letters) are used.
If the ratio is not 1:1 (or is not known), the prefix  (+)/(−), - or d/l- (with a slash) is used instead.
The usage of d and l is discouraged by IUPAC.