How do you tell if your 1920-D Mercury dime is a VF or one of those symbols and how much do you think it is is worth?

"Those symbols" are abbreviations for the grade, or state of preservation, of the coin and range from Poor (you can tell it's a Mercury dime, but that's about all) to Mint State (just like it was when first struck). There is a book that may be available in your library called Photograde. It has pictures of all the US Coins in each grade and describes the detail that should be visible in each grade. Any fair-sized public library will have a copy of A Guide Book of United States Coins. This book has a very brief description of the grades for each coin and values for the coins in different grades. DON'T assume these values are current. Prices can change quickly sometimes and since the 2006 edition is probably already being printed it will be six months behind when it gets to the bookstores. Your 20-D will probably be somewhere between $2.40 and $15 in circulated condition. There is an online grading guide for Mercury Dimes here : http://www.coincentric.com/GradingMercuryDimes.htm There is an online retail price guide for them here : http://www.numismedia.com/fmv/prices/mrcdim/pricesgd.shtml