I remember, in one of my earlier projects, we had code quality metric which used to run after each fortnightly build and integration. This tool used to count no. of global variables added to C and public variables added in C++ source code. Even if single such variable is reported, author of that code had to justify use of global/ public variables.

P.S. That doesn't mean there were no public/ global vars in legacy code. This practice started when code quality and system stability gradually started declining by their overuse