Staff engineer is the title most organizations get wrong, because it is the easiest one to hand out for the wrong reason. It looks like a reward for sticking around and being individually excellent. It is not. It is a different job, and the people who are great at it are doing something most senior engineers are not.
Here is what I actually look for.
They make other people better, structurally
Not through mentorship, or not only. Through the systems they leave behind. A staff engineer changes how a team works, so that the team is better even when that person is on vacation. A senior engineer who is merely excellent makes the team better while they are in the room. The structural version is the bar.
They are drawn to the ambiguous problem
Give a strong senior engineer a well-specified hard problem and they will do beautiful work. Give a staff engineer a vague, political, half-technical mess that nobody owns, and they will go toward it, because that is where the leverage is. The willingness to operate without a spec is most of the job.
They can be wrong in public
This one sounds soft and is not. Staff engineers have wide influence, which means their mistakes propagate. The ones I trust are the ones who will say “I was wrong about that” clearly and early, because an org that punishes that produces staff engineers who quietly defend bad decisions instead.
What I do not weigh much
Tenure. Raw technical depth past a high bar. The sheer number of systems they have touched. These are all real, and none of them is the thing. The thing is leverage: does this person make the teams around them permanently better. If yes, the title is describing reality. If no, the title is just creating a future conversation about why reality does not match it.