What is it that makes an autograph special, valuable, or desired? Does it need to be rare, or can it simply be from someone notable?
The answer, Pete Rose proves, is either.
To start, a Rose signature is not rare. Since being banned from the game many years ago, he has built a business, Hit King Inc., entirely based around selling signed memorabilia--and limiting the supply to increase the price is not part of the strategy, which appears to work quite well considering he regularly clears $10,000 in a single day.
Rose does live signings on the Las Vegas strip for 15-25 days a month, where he waits at a booth and will briefly meet with fans if they purchase memorabilia and a signature. For an additional fee he will also inscribe custom messages, often being asked to add tongue-in-cheek historical references such as "I'm Sorry I Broke Up the Beatles", a practice that more recently led him to being unintentionally portrayed as supporting certain political candidates.
His website, PeteRose.com, offers books, bobbleheads, jerseys, banners, and photographs, all bearing his "John Hancock" and clearly listed prices. Googling "Pete Rose Autograph" will prompt shopping results from Kohl's, Groupon, and Newegg. You can even purchase a signed "I'm Sorry I Bet on Baseball" ball on from Walmart for a bit over a hundred bucks.
What this means is that it's only slightly harder to find a Pete Rose signed baseball than a regular baseball, and determining the value of commonly signed gear is fairly simple with so much readily available price information.
Of course, rarer or harder to duplicate items may still see the higher values associated with celebrity memorabilia.
If the signature is on an All-Star game home plate, or an Andy Warhol print, you can expect to see that reflected in the price.
Ultimately, you don't need to be a sports memorabilia guru to assume that Rose's signature, in and of itself, will not demand a hefty price tag. And while it can be assumed the "Hit King" sells plenty of pre-signed gear, much of the buyer's appeal is getting to see and meet the man himself. This may be part of the reason that despite completely saturating the market, the set price for a Rose-signed baseball (typically $60-100) has actually seen an increase over the past decade.
His autograph may be more commodity than rarity, but it is a commodity with a steady and constant demand.
So, does Pete Rose have a valuable signature?
From the perspective of a sports memorabilia collector, not usually.
From the perspective of Rose's accountant?