I have worked on a couple of Ackley's rifles over the years, still have the barrel off of one that I replaced several years ago. I do not see a signature on it, and have never seen one, not to say he didn't do it, just never seen it. He did have a stamp for his name that is common on all of them - that I have seen. It usually reads P.O. Ackley and then under that the caliber it is chambered in. your stamp looks just like the one on the barrel I have - and have seen.
I just couldn't get rid of the barrel, too much nostalgic memories of the man to trash one of his barrels, even shot out . . .

I started building rifles back in the mid 60's and Mr. Ackley was still alive - he was the man . . . Had a good friend that moved to Idaho and lived about a mile or so from him, he used to tell me stories about his visits with him, at that time Idaho was the other side of the world . . never got to meet the man, but read nearly all his books, still have them.

I now wish I had ask my friend to get some signed copies from him . . wow would that be a treasure . .