If you notice that the opposite team's runner missed a base, don't look for the umpires to call that out -- this is an appeal play and the umpires are supposed to show a "poker face" when this happens. Here's how to properly get that runner out:

1. If the ball is live, have one of the fielders step on the missed base or tag the runner (if they are still on the field). The fielder should indicate what they are appealing, for example they should point at the player and loudly say "thirteen never touched home!"
2. If the ball is dead (for example, the runner advanced on a dead-ball award, such as a hit-by-pitch or a ball out of play, and never touched home), then the ball must be put into play first:
   1. Return the ball to the pitcher.
   2. Once the pitcher is engaged and the umpire says "play!" the pitcher should properly disengage by stepping backwards from the rubber with their pivot foot (the foot opposite their glove hand).
   3. Once properly disengaged, and before making any other play, the pitcher should touch the base being appealed, or pass the ball to another fielder who will do that. They can also tag the runner, if that runner is still on the field.
   4. The fielder making the appeal should indicate what they are appealing ("thirteen never touched home!").
   5. Careful! If the pitcher balks while disengaging, that counts as a "play" and you lose your chance to appeal.

At this point, the umpire will either call the runner out or safe. Unfortunately, with a two-umpire system, it is possible that neither umpire saw what happened, because their attention was on something else (c'est la vie). In that situation, they must rule the runner safe -- even if every coach, player, and spectator is swearing to them that they saw it happen.

So, TLDR:

1. Umpires will never say anything, you must make an appeal play.
2. A fielder holding a live ball must touch the base being appealed (or tag the runner).
3. The umpires need to know exactly what you're appealing.
4. If they didn't see it happen, they don't have a choice but to call the runner safe. Accept it and move on.