With some medias you can tell (verbatim 16x+r is always mcc004), with some you can tell from the country of manufacture (sony 8x+r made in japan is yuden00t02). With some you can tell from markings on the package or particular package styles. With many, there is no way of telling till you open it and read it off the disk.
Also, as pinto2 posted, you can go to videohelp and find out what diffrent medias it may be. Personally I usally stick to medias that I know (or have a high probability) of geting the media code I want.
Is there are particular media code you are looking for?