According to this resource, names were generally stitched into the collar:
https://mlbcollectors.com/BOSjerseys.php
If it's an actual autograph, it probably wasn't put there while in use because teams washed jerseys after each game and an autograph would've washed out. But if it's in indelible marker, then it could've been written for game use instead of tagged in the collar, either at the major or minor league level.
Or, there could've been a collar tag that was removed when the shirt was sent to the minors, with the new owner's name written into it. Or... it could've been signed by the player after it was no longer in service.
If you could post a picture it would be very helpful.