Ok this maybe a stuipd question but did the 1964 Jefferson Nickel's not have a mint mark on them? I have one and for the life of me i can't find one on it. Here's some pics:
What you have is a Philly minted coin. The Denver minted coins have a D on the reverse just to the right of the building.
Philadelphia did not begin placing a P mintmark on its coins (with three exceptions) until 1980. The exceptions are the 35% silver war nickels 1942-45 that had a P over the dome, the 1979 P SBA dollar, and the fact that the cents struck at Philadelphia still do not have mintmarks.
You know ShoeK, if we didn't ask what we think are stupid questions, then we wouldn't learn anything from the ones who know the answers. jeankay
It's all part of your education. You are not born with this knowledge. The best way to gain this knowledge is to educate yourself by reading, asking questions and listening to other knowledgeable people (like here at CoinTalk).