Use -Wsign-conversion flag for clang to warn implicit sign conversion.

int main()
{
    unsigned int x = -1;
    return 0;
}

$ # M1 Mac (Ventura) + Apple clang 14.0.0
$ clang sample.cpp -Wsign-conversion
sample.cpp:3:22: warning: implicit conversion changes signedness: 'int' to 'unsigned int' [-Wsign-conversion]
    unsigned int x = -1;
                 ~   ^~
1 warning generated.

Suppress warnings

Use -Wno-sign-conversion to suppress warnings. It can be used to cancel -Wsign-conversion if already set.

$ # M1 Mac (Ventura) + Apple clang 14.0.0
$ clang sample.cpp -Wsign-conversion -Wno-sign-conversion
$

References