I think Levels.fyi must make it clear on their website that the number viewed is annual bonus. Usually, when negotiating, you're also negotiating your sign-on bonus. They can also include it as another column.

A lot of people are putting their sign-on bonus amount as their annual bonus. I can tell because the number for the company I work for are almost identical to what each level usually get.

The longer Level.fyi waits to fix this, the compounded the problem become.