It depends on the gun. My Merwin Hulbert looks to be hand stamped with a center punch there are about 30 punch's a letter. I have seen some colts 1903 for example looks to be engraved with an italic font. Most look to be stamped with some style machine as the Detroit Police looks perfect and numbers look a little uneven.

No I have never come across a model 22 .45 DPD marked gun never knew one existed as Detroit was never a big Caliber city. mostly .32, .38 I will get some pictures of guns up soon.