An additional layer of encoding is provided using conventional one-dimensional (“1-D”) bar code symbology. Dark bars of at least 2 heights are used (where the dark bars may be narrow or wide, and may be separated by a space that is narrow or wide) for 2-dimensional (“2-D”) encoding. Whereas the width of the dark bars is significant in the 1-D encoding, the height of the dark bars is significant for the 2-D encoding. In one approach, dark bars of a shortest height are used for encoding conventional 1-D data, while dark bars of other heights encode additional data in a 2-D portion of a bar code. In another approach, consecutive dark bars are used in combination, according to a mapping which correlates the various combinations of bar heights to respective characters. The 2-D encoding rules may be proprietary, providing a type of data privacy.