https://www.answers.com/us-history/Is_a_penny_with_no_mint_mark_rare
Is a penny with no mint mark rare? - Answers
Almost never. Remember, while Philadelphia has used a P mint mark since 1980 on most coins, cents from Philly are still "plain"; i.e. they don't carry mint...
no mint markpennyrareanswers
https://www.answers.com/other-math/What_if_there_is_no_mint_mark_on_your_silver_dollar
What if there is no mint mark on your silver dollar? - Answers
No mint mark means it was minted in Philadelphia.
no mint markwhat ifthere is