Magic: the Gathering History, Set Symbols, and Set Lists
Sometimes called "the granddaddy of collectible card games" (helping to spawn games like Yu-Gi-Oh! and Pokemon), Magic: the Gathering has been around since 1993, and has produced a myriad number of expansion sets since its inception. With hundreds of thousands of cards to choose from, five basic philosophies of winning, and many deck ideas still undiscovered, you too can build a custom 60-card deck of your own and join the party!
Card Rarities and Set Symbols
Up until Exodus (at left), commons, uncommons, and rares were not color-coded (rares didn't even exist for a while in the game--there were Uncommon 1 and Uncommon 3 instead). When Exodus came out, there was suddenly a color-code: commons had the set symbol printed in basic black and white, while uncommons had it in silver, and rares had it in gold, as shown.
Within Time Spiral (at left), there were cards designated with a special purple-shaded set symbol--this symbol means that it is a direct reprint of an older card. Time Spiral reprints can sometimes be of less monetary value than their original versions, but what the reprints did was reintroduce the older cards into Type II (Standard) play for the Time Spiral block, exposing newer players to past strategies. Purple-symbol cards are treated as something "other than" rare, but equally as valuable.
The symbol color code got another addition with the Shards of Alara set--a new class of rares called mythic rares were introduced. Mythic Rares are a class beyond rare because of their strength, and they are very hard to pull from packs. These cards had the set symbol printed in a vibrant red-orange, seen at left.
Set symbols screencapped from CrystalKeep.
Note: Some of the earlier sets have no set symbol--you have to check the date on the bottom center of the card to see what set it might have been printed in. Gatherer is also a good resource for learning what set a card was printed in. Revised, Unlimited, 4th Edition, and 5th Edition all looked alike to me at first, but in most cases the printed year date will tell you which set it is. (Hint: Revised has just an "Illus. by (artist name)" line and no year listed; Unlimited has REALLY BIG text in the text block.)
Expansions and Special Sets
For up-to-date information on all the Magic sets and their symbols, check MTGSalvation's Expansions and Sets wiki. If you've got a card with a symbol that doesn't match any of the named expansion sets, check the special box sets list, since those have their own symbols.