TODO, FIXME and XXX are built into tools already. Sure you can make new stuff up but it makes it harder to find later.

Those things are configurable, though, so new markers are rarely problematic from a tooling perspective. Getting your teammates to agree on using the same markers is perhaps the bigger problem.

Making them agree is not necessarily the hardest. But remembering to tell new team members in a year or two. Or revisiting the codebase in 5 years from now. I doubt you'll remember