I try to educate myself on any coin in question before I put the issue on coin talk. Couldn't nail it down, so here goes. Did the U.S. mint issue a 1938 no mm Lincoln cent ? This coin stands on it's edge on a flat surface. Doesn't appear to have the beveled edge a circulation strike. Also has strong devices.

Yes, they did issue a 1938 proof with no mint mark. To answer your other post..."Flat" is a relative term. Some edges are flatter than others, some coins will stand on edge, while others will not. Your coin is a business strike, not a proof. Your other pic shows a slight variation along the rim to show this. If it was a proof it would have much more squared rim.

All proof Lincoln's until 1964 had no mint mark. In 1968 proof minting went to San Francisco. A proof 1938 will have a mirror finish with flat rims on the bottom as well as the sides. The edges will be squared, not rounded. The 1938 you posted is not a proof.

You can usually tell a proof, even impaired (circulated) because they look different, and great, with a lot of luster and sharp details. As well as squared rims.

I recommend you purchase a copy of the 2020 Red Book, which has lots of information about all US coin types, including talk about what a proof coin is.

Proof coins have an edge that meets the face of the coin at a 90 degree angle. Your coin does have a flat edge, but you can see where it rolls off toward the face.