"My uncle ran an ice cream franchise for many years from the 50's through the 80's and saved coins he thought might be valuable. I was going through some coins he left me after he died, and one of them is a 1945-P nickel. It has a large P on the back. But, there was another 1945 nickel that came with it and it has no mint mark at all. I Googled this and found your article:

"The E-Sylum: Volume 7, Number 13, March 28, 2004, Article 9, COUNTERFEITING CIRCULATING COINS." However, this deals with a 1944 counterfeit, not a 1945. Do you have any information on a mintmark-free 1945 nickel?"

Francis LeRoy Henning, aka "Henning's nickel"

He was in great need of a good five-cent cigar.

I looked at the images and the 1944 is a "genuine" Henning counterfeit (weak detail on Monticello, copper-nickel color), but the 1945 nickel is a normal Wartime silver nickel, as you can tell by the color. I believe that I can see traces of the mintmark over the dome, though it is quite weak. (Take another look).

Regarding Henning, though, according to an article in Coin World August 28, 1968, p. 33, Henning is known to have made dies with five different dates: 1939, 1944, 1946, 1947, and 1953. (He was afraid that tellers might become suspicious if all the deposits he brought in had the same date.) No 1945 is known.

Of these, the 1944 is the most obvious because it lacks the mintmark and is the wrong color. But the others can be recognized too; this article illustrates one of the 1939 counterfeits. All the Henning counterfeits can be positively identified though weak reverse detail, rough surface, and (in some cases) diebreaks.