Vocalization is key.
You gotta let people know you would like to get next game. Otherwise how are they supposed to know your not just watching the game.

I try to be courteous and if I saw someone standing there (especially a kid) I would ask if they wanted next game. Not everyone is like that though. Doesn’t meen the dudes a dick. Pinball is full of socially ackward people that may not initiate that conversation. Be proactive.

Now that being said, I have no issue calling people out that are game hogs.
I’ve even seen people at conventions do shit like start a 4 player game all by themselves so they don’t have to get off a machine while other people are waiting. I have no problem standing behind them and making comments about their poor etiquette, especially when there are kids waiting in line.