#include <stdio.h>

#define STR(x) #x

int main()
{
  printf("%s", STR(\u0024)); // UCN for $ was allowed, now it is not
}

and


#include <stdio.h>

#define EAT(x)

int main()
{
  EAT(\u0024) // UCN for $ was allowed, now it is not
}