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> Several major cities in the US use these in their taxi licensing systems, including New York City, Boston, Cambridge, Chicago, Philadelphia, and San Francisco.

I think you might have misinterpreted the sentence here: these are cited as examples, not at the only cities in the US to have such a system in place.

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Did you research before asking "which cities didn't?" Or only after I replied?

"Denver taxi medallions" seems to return nothing indicating they have one.

Los Angeles doesn't seem to have one either

Is "medallion" a requirement for this search? I think a lot of cities that use this system merely call them licenses. I'm not sure that whether you call the system one of medallions or one of licenses makes them qualitatively different if the principle is that a) only a limited number can ever be issued creating artificial scarcity; b) that scarcity and resulting high cost create a protected group of suppliers; c) the city has a financial interest and even duty to shield the market from competitors and innovation.

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