SPDX standardizes how source code conveys its copyright and licensing information. See https://spdx.github.io/spdx-spec/1-rationale/ . SPDX tags are adopted in many large projects, including things like the Linux kernel.
Macros should be all upper-cased. This is also kind of a wart that's been sticking out for quite a while now (we avoid prefixing underscores).
