From Charm Cities Wiki

The monetary unit of Charm Cities is the spesmilo, abbreviated . The symbol is used before the number (e.g. ₷12,000), at least for English editions of the game. The value of the spesmilo is the same order of magnitude as that of the dollar, euro, or pound, but there's no exact one-to-one relationship to either.

Both the name and currency symbol are taken from the real-life spesmilo, a short-lived international currency invented by the Esperantist movement, but there's no further relationship to the real-life currency. The plural of the game currency is spesmilo, not "spesmiloj" as it would be in Esperanto. They were chosen because they're clearly distinct from the SimCity § for "simoleon" (the best name for a video game currency yet chosen) and the Cities: Skylines ₡ for "cell" (I didn't know the name until I looked it up just now; it's not very good), because "₷" is a Unicode character that should display on most machines, and because the symbol isn't in current use (unlike ₡, which must be somewhat confusing for Costa Rican players).