I don't always have an internet connection to research the rarity of a MTG card. Is there an obvious indication of rarity on MTG cards themselves (other than foil)? Some sort of insignia? Or a class of creatures that is almost always rare?
Yes, cards have a rarity indicator (at least in recent years). Each Magic card has an icon below and to the right of the picture called the expansion symbol, which indicates the expansion set that the card is from. The icon's color indicates the rarity of the card, with the following key:
- Black: Common
- Silver: Uncommon
- Gold: Rare
- Red: Mythic Rare
To get an idea of the relative rarity of these cards, we can look at a booster pack. Recent booster packs each contain about 11 commons, 3 uncommons, and 1 rare, with about a 1 in 8 chance of the rare being replaced with a mythic rare.
A couple of things to remember: very old cards, like from Alpha and Beta, don't have expansion symbols at all. Other old (but not as old) cards have expansion symbols, but they're all black. And some cards have been printed in different sets, and have different rarities in those sets, so the icon on the card may not match the rarity in the most current set.
these answers are correct but simply evaluating the card’s strength is a good indicator of its rarity. weak cards are common, useful cards are uncommon, strong cards are rare and overpowered cards are mythic rares. mana cost is also a good indicator for its rarity: a card that is strong and does something unique is usually a rare even if it has a high casting cost but for example a card that seems nice but is more of a useful card (strength of an uncommon) but it has casting cost of only 1 or 2 is likely to be a rare! of course the rarity comes from how rare or common they are in a booster pack.. this means that some cards are marked as common in other sets while they are uncommon in other sets! and because rarity isnt actually tied to its strength but its commonness, a really strong card could be marked as a common while some really weak card as a rare and for this reason i often argue with myself that some uncommon card is as strong as a rare or vice versa and fair enough i often do find out that it has been printed in that rarity (lightning bolt for example: costs 1 red mana and does 3 damage to target creature or player.. its nothing special so its a common, but its actually pretty strong for its mana cost and thus really useful! and it is infact a common in some sets and an uncommon in some others!) TLDR; the card’s strength is a good indicator
if you are looking for its actual rarity in the world, you should look for its price (though that requires internet) and the price is mostly a matter of its competitiveness as more powerful cards are more wanted and people are willing to pay more for them.. also the older the card is (or brand new) the rarer it is. so putting these together: strong old card (and if its legal in some format), the rarer thus more valuable it is
PS. newer cards that are standard legal usually become cheaper when they cycle out of standard format because they are not useful in modern or other formats