I think it leans more on the side of being good, although I do see a few things that are a little off. The loop of the A is a little stronger than most examples I've seen, and at first I was concerned a bit by the straight top r in Arnaz, but it appears that he signed that letter that way and another - perhaps one was earlier or later in life. It also looks like he always doubled over a part of the last a in his name. The loop of the z looks the same in several also.
From those exemplars I am not seeing his hand - the slants as Joe mentioned for one thing. Look at his baseline. Let's see what Joe sees. click for full image.
It could be a later in life very slow signature although I do not like the slant, his "D", along with the, what appears, the slow handwriting. I haven't studied Desi in a number of years. It just jumps out, to me anyway, one I would shy away from.