I haven't paid enough attention at baseball games. At hockey games, if you can see the scorekeeper, they have a lamp at the glass that will come on during a stopage to let the refs know it's time for a commercial (if you watch for this, you can get a jump on the crowd if you need a bathroom break or refreshments). You can usually predict a commercial timeout, they've got guidelines that are pretty consistently applied [1]
I meant to also say that the light doesn't go off until the commercial break is done, so they don't drop the puck before the broadcasters are ready. Typically an off-ice official holds a door open and stands in it to also signal not to start, if it looks like everyone is ready to go a bit early.
I haven't paid enough attention at baseball games. At hockey games, if you can see the scorekeeper, they have a lamp at the glass that will come on during a stopage to let the refs know it's time for a commercial (if you watch for this, you can get a jump on the crowd if you need a bathroom break or refreshments). You can usually predict a commercial timeout, they've got guidelines that are pretty consistently applied [1]
[1] https://nhlofficials.com/know-the-rules/week-20-need-a-break... search for "Commercial’s time-outs should be taken at the first whistle"