When I was in High School - I idolized Nolan...he was in his early 40's then and still throwing no-hitters against great teams like the early 90's A's...
Anyway, I sent Nolan a page letter asking him questions about his two seam fastball and his circle change.

About a month later, I got my SASE back with my card untouched - but a postcard was inserted in there with a note saying something about "too much fan mail, but please accept this autographed card for taking the time to write me..."

I kept that card for years - and sent it in to PSA just to have it encapsulated and protected. Turns out - it was an autopen signature. Well - who could blame him? He was probably getting hundreds of letters every week. The fact that he sent something back (or his staff) was at least courteous. That was the only time I ever wrote to an athlete.