Reading the dollar sign in Mexico: a guide for pesos and dollars

Start with the default: in Mexico, $ is the peso

Mexican consumer law settles the everyday case. Article 34 of the Ley Federal de Protección al Consumidor says product labels and advertising must show the price en moneda nacional, in the national currency, in Spanish. A store can add another language or another measure on top, but the peso price has to be there. So a $ on a shelf tag in Mexico is a peso price unless something tells you otherwise.

Contracts work a little differently. The same law lets a consumer contract state amounts in foreign currency as well as in pesos. And the Ley Monetaria, Article 8, says foreign currency is not legal tender in Mexico except where a law says so. A debt written in dollars and payable in Mexico can generally be settled in pesos, at the exchange rate in force at the place and date of payment, under rules the Banco de México sets. There are exceptions, including some bank deposits, so read your own contract before you rely on that.

How to tell the two apart on a page

• MXN is the Mexican peso and USD is the U.S. dollar. These are ISO 4217 codes: the first two letters are the country, the third is usually the currency.
• Mex$ means pesos. US$ or USD means dollars. If a tourist-facing site shows a bare $, look for a currency switcher or the fine print.
• The words moneda nacional next to an amount mean pesos.
• Inside the United States, a bare $ is assumed to be U.S. dollars. Canada, Australia and many other countries use the same sign for their own dollars.

One more quirk: the one-stroke and two-stroke versions of the sign are usually treated as the same character. Unicode gives both a single code point, U+0024, and the difference is mostly down to the typeface.

Why the peso has the older claim

The symbol goes by two names, dollar sign and peso sign, and the second one is at least as honest. The earliest uses turn up in 1770s business letters from the West Indies, where it stood for the Spanish American peso. The most widely accepted theory says it grew out of the scribal shorthand "ps" for pesos, with the s gradually written over the p. The U.S. dollar was later modeled on that same coin. In other words, Mexico did not borrow the symbol from its northern neighbor. The symbol followed the peso north.

Historians still argue about the exact path. A pillars-and-ribbon design on Spanish coins, a mint mark from Potosí, and a German silver-coin sign all have supporters. We could not find a single documented first use that everyone accepts, and anyone who tells you otherwise is guessing.

The N in MXN is a leftover from 1993

The code has a better story than most. On January 1, 1993, Mexico introduced the nuevo peso, worth 1,000 old pesos. The decree required new notes and coins to carry the words "nuevos pesos" or the symbol N$ until the old money was withdrawn, after which the "nuevos" was to disappear. It did. The N stuck around in the currency code anyway: that final letter reflects the 1993 revaluation, and the older code was MXP.

My favorite detail comes from the Banco de México's own archive blog. To explain the change, the bank printed a "folleto popular," a small fold-out leaflet, under the slogan "Nuevo peso, más práctico y más sencillo." It went out through post offices, Metro stations and Profeco offices, and it was translated into Maya, Zapotec, Náhuatl, Tzotzil, Tzeltal and Chol. A currency reform that bothered to speak to people in six Indigenous languages seems worth remembering every time someone squints at a price tag.

So when you see $180 in Mexico, assume pesos, check the code when money is serious, and enjoy the fact that you are reading a symbol the peso wore first.