On the lower left front of the card you see the 4 diamonds in black, those indicate the "rarity" of the card and that it is a 4 or quad diamond card. If it was a single diamond card only one diamond would be black the rest would be hollow outlines or not there.
Here is a single diamond card someone is selling on ebay. If you look in the lower left corner you will see the difference. Here is the link: http://www.ebay.com/itm/11-12-BLACK-DIAMON...=item3f2b93734c
You can also go by card number. This set generally runs that the base are all single diamonds generally 1-90 (only one diamond blacked in or shown depending on year), the double diamonds go from 91-130, triple diamonds are 131-170, and then the quads are from 171-210. Some sets have a different numbering scheme, but the majority run in these types of ranges with the highest card numbers being quad diamonds which are the "best" rookie prospects and superstars like Gretzky, Howe, Orr, etc.