Relic cards from Topps are a specially designed series of collectible trading cards. These cards are issued in limited editions, causing their overall value to greatly inflate over time. Whether you're trying to identify if a card in your personal collection belongs to the "Relic" line or if you're trying to find out more about the line in general, you can use the Internet as your guide.
Look on both the front and the back of the card for the Topps "Relic" logo. Certain cards in the "Relic" series of collectible cards are marked with the word "Relic," making them easy to identify. Relic cards are almost always cards that feature older players like Babe Ruth or Mickey Mantle, so if you have such a card that also has the "Relic" logo then you have a Relic card.
Go through the detailed breakdown of cards released in a particular year on Topps' website (topps.com). Topps maintains a list of all the cards released during a particular year, and also lists what new "Relic" cards are going to be available. This can help identify cards in the line that are not marked with the "Relic" logo but still fall within the collection.
Find your card in a price guide, either in print or online. If you aren't quite sure whether you have a "Relic" card and you want to find out more information, write down the name of the player on your card, the name of the series the card belongs to and the year the card was released (all information that is on the card itself). Look up the card in a price guide, which will contain information about whether or not the card is a "Relic" card.