Illegal Ball

[Steve M]

Balls that go out of play are returned to me, and I check them before putting them in the ball bag. In my pregame instpections, I will mark that game balls so that I know they are legal as the game goes on & the writing is scuffed off. As long as I see and/or feel my initials in the area I put them, I know I've got one of the ones I started the game with. If my initials are not on the ball, it had better be new enough that I can see compression & COR & anything else I need to see for that particular sanctioning body.

Addition:
As to your situation, your plate ump "assumed" the ball to be legal & so did the pitcher. That's a homerun as you now do not have any way of being sure the ball you are now being shown was the one that was hit out.