Index -> Interface -> Filters & Search Options -> Collector Information

On the bottom edge of every Legends of Norrath card, you'll find information to help you identify its rarity and the set it comes from. The first number tells you which set the card comes from (1 is Oathbound). The letter tells you the rarity of the card (R is rare, U is uncommon, C is common, and F is an avatar card found in starter decks or a reward card for completing a scenario.) Last is the number for that card in the set.

Some cards have a P for their rarity, marking a special Promo card separate from (but related to) a normal expansion set. These cards are made available in a variety of ways, including gifts to subscribers, rewards for high-level tournaments, and more.