Welcome to LCR. From 1950 to 1964, Lincoln cent proof coins were produced at the Philedelphia mint (no mint mark). From 1965-1967 there were no proofs made. From 1968 to present, proof Lincoln cents are made at the San Fransisco mint (s mint mark). The only year that the mint made a mistake, I believe, was 1990. Only a few coins were struck without the mintmark. Very rare. I suggest very highly that you purchase a "red book" on us coins. You can buy one online or any major book store. The latest edition is 2012. The other thing to do is visit a coin store or local coin show. You will be. Able to see for yourself what a proof coin, etc., looks like in person. Pictures are sometimes deceiving. If you private message me with your address, I will send a proof Lincoln Cent to you at no charge. Get that red-book and read the whole book. It's not only a reference on us coins but ties the history of the US into the book too.
Good luck and remember that if you don't ask questions it's hard to learn. We are here to help! And sit back and whatch how the forum works and what is being posted. By doing that you will also learn alot.
""Time and Tide wait for no man"