since this thread had been brought back twice from a twelve month-plus slumber, I see no problem bringing it back after a couple months (due to my inactivity here);
The magnetic ones have the crown mint mark. The non-magnetic ones have a "p" mint mark. And one guy claims to have a bunch that have the wrong mint mark, but are magnetic... here's the link I found for it.
I am sorry but you are in error (punn intended);
up to about midway through the 2006 mintage run, the zinc coins had no mint mark, while the plated steel coins had a 'P' mint mark;
About midway through the 2006 mintage run, all coins started using the RCM
logo where the 'P' was previously seen on plated steel coins;
For the first half of the 2006 mintage of pennies, there were some zinc blanks that got mixed into the steel blanks - so some 2006 "non-magnetic" zinc core pennies have a 'P' mint mark;
There were also some zinc blanks that got mixed in with the steel blanks.
What I found rather exciting about the 2006 pennies, was that there were four official variations on the coin - and two unintended error variations:
1) zinc core, no mint mark
2) steel core, 'P' mint mark; very low mintage
logo, zinc core
logo, steel core
5) steel core, no mint mark; error coin; rare
6) zinc core, 'P' mint mark; error coin; exceptionally rare.
I have examples of what I numbered as #1 through #5;
I do not have a #6 penny.
I also never made a spot for a 2008 zinc core penny in my book, as I understood from this thread that the coin was exceptionally rare...
After reading the linked story, I can't help but wonder if the errors were because the dies were changed out before the correct blanks were used up - this is what I previously assumed, but changed my "song" after several sources which I assumed to be reputable, said that it was a matter of the blanks getting mixed up.