Mumzie,
I have to agree with Gene on this one (among others). We know when it's an "alley" ball and when it's an old ball that belonged to someone, who, for any number of reasons saw fit to "dump" it on the rack. I've left many balls myself and I know others have found value in those balls and took them home to be redrilled. They were NOT owned by the house. I never found anyone who wanted those balls I left on purpose, but knew someone, who I didn't know, might come across it. There were other balls that I didn't care what happened to them.
You should NEVER place your personal balls on a house rack for just that reason. I'm not sure why you thought it was safe to do that. If I'm not using a ball, it is either sitting in the settee area on a chair or it's in my bag.
Yes, if you steal rental shoes or an alley/center-owned ball, you are a thief. If you take an old personal ball that someone left on the house rack, you are NOT a thief.