1967 no mint mark....it's possiblity a ddo it has some other letters on the obverse side that I think could be a light die clash but I think it's either a ddo or a possible proof .. Can anyone help me with the coin
if you do some basic checks like from this website https://www.usacoinbook.com/coins/small-cents/lincoln-memorial-cent/ you'll see there was no Proof made, and also only made in Philadelphia. Since Philly was the first and at that time the only mint to make coins, they didn't have a mint mark because there was no reason to differentiate the manufacturing location.
Time for you to buy and use the R. S. Yeoman Red Book. No proof sets were issued for that year. Spend it or plug a hole in the Whitman’s folder.