Reveal your sources.
That’s one of the best, most impressive, gifts you can give a former player. Don’t just say, “I read about you.” If you quoted a fact from http://www.baseball-almanac.com/, such as a uniform number, say so. You don’t have to send a bibliography. Just show that you’ve gone the extra step.
I’d guess that some retirees, even those Internet users, might believe the only details about their career are limited to statistics or a wikipedia entry. I’m pleased every time an ex-player responds with a thank-you note and “I didn’t know that!”
A 79-year-old former Cub printed off a two-page feature about himself that he found on the ‘net. He included this with his page-long letter.
Some guys might not be signing for everyone. Compete. Stand out. Show each person you write to that you’ve done your homework.