I have a score card signed by former Tiger's broadcaster Ernie Harwell. -It was a score card he used during a Tigers-A's game in 2000, I believe. Really neat to see his handwritten notes and scribbles.
One time (in 1988 or so) I saw Darrell Evans at a local park and he was looking for his keys in the parking lot. He offered me $5 if I found them, so the search was on! Unfortunately, I didn't find his keys, but I got him to sign a Kroger's (grocery store) receipt my mom had in her purse. Still have it.