Welcome Morgan63, generally if there is no mint mark on the coin it was minted at the Philidelpia mint.
Can you give us a little better description than "a few coins". It would be of help to know the year and denomination of the coin. Pictures would even be better.
True for U.S. coins (for most years - think 1965-67 ), but ancients generally lack them, and in many countries most or all coins have no mint marks. In some countries, symbols (like the Spanish six-pointed star) rather than letters, are used, which are unrecognizable as such to people unfamiliar with the particular country's coinage. In his initial post Morgan63 did not say "US coins", so realize that in the 2006 Krause it takes 2,335 pages to cover 20th/21st Century coins, of which only 37 are devoted to full coverage of all U.S. coins, including commems and bullion. BTW Morgan63, welcome to the forum.
True, but he did post this in the US coins forum, so that would be the logical guess as to the coins' nation of origin.
All the coins are from the U.S. and the date and demonitions are as follows: Quarter~1974 Nickel~1975 1963 Cent~1987
