Every city’s transport company has its own system of timetables and of informing travelers when the next bus or train can be expected.
In Paris, you raise your eyes to the sky to have the answer. (Unless you check the transport company’s app on your smartphone.)

Why the sky? It’s word play. The French word for sky (and heaven, by the way), is ciel. The information system on the Paris public transport is called Système d’information en ligne, acronym SIEL, which is pronounced almost the same as ciel.

SIEL captures the next two métros or buses in real time, so next time you are at a Paris bus stop or metro station, raise your eyes to the SIEL, it will provide the answer.

For good measure, here’s one you really don’t want to see: