Checking string occurrences at compile-time

I am trying to solve a problem where I can define a class given an std::string only once, or else the compiler will throw an error.

Example:

Suppose we have a class Car which is initialized with its license plate. When creating it, the compiler is supposed to check if a Car instance with the exact same license plate string has already been created before.

My approaches so far:

I have been looking around for template-metaprogramming solutions which should create a simple registerable counter (example), however I fear that this doesn't really fit my needs.

Another idea was to create a simple define including the given license plate string, which but of course are unable to be created at compile-time since the license plate string is being passed only at run-time.

#include <string>
#include <vector>
#include <algorithm>
#include <iostream>

std::vector<std::string> myGlobalVector {};

class Car {
public:
  Car(std::string const& licensePlate);
  ~Car() = default;
  // ...

private:
    std::string _plate;
};

// ...

Car::Car(std::string const& licensePlate)
{
  // this would be the runtime version of what I want to achieve:
  const bool alreadyExists = std::any_of(
        myGlobalVector.begin(), 
        myGlobalVector.end(), 
        [&licensePlate](std::string const& otherPlate)
        {
            return otherPlate == licensePlate;
        });

    if (alreadyExists)
    {
        std::cerr << "License plate already registered. Exiting." << std::endl;
        exit(-1);
    }

    myGlobalVector.emplace(licensePlate);
}

int main() {
    Car someCar { "A4EM21F" };
    Car anotherCar { "F121EG4" };

    // ...

    // this should throw a compile-time error as 
    // given string has already been used before in this context
    Car lastCar { "A4EM21F" };
}

My only idea so far (which obviously won't compile but is supposed to illustrate what I want to achieve):

// ...
Car::Car(std::string const& licensePlate)
{
#ifndef CAR_##licensePlate
#define CAR_##licensePlate
    _plate = licensePlate;
#else
#error Car has already been created in your code!
#endif
}
// ...

Can anyone think of a way to check the occurrence of a string in a code snippet at compile-time?

I woult be grateful for helpful hints using any kinds of template-metaprogramming, type-trait or other topics.