What's a strong signal in your experience?
Plus, nervousness and comfort with the environment and questions makes the error bars bigger.
Depending on the level, but assuming a Senior role, then some stronger (not strong, just stronger) signals are:
- ability to code basic solutions in the language of choice - ability to reason about code complexity
- ability to get to a solution
- ability to explain their reasoning
- demonstrate they understand the nuance and complexity of software development
- understanding common tools in the domain they are interviewing for (sharding for distributed systems for instance)
Same, but on the negative/bad side of things:
- arrogance, argumentative, rude (nervousness is totally fine and expected)
- one true way-ism
- complaining about interviews during an interview
- inability to solve basic coding questions
- lack of understanding about basic data structures (too many people I've interviewed don't even understand how a hashmap is used)
The places I've worked in the past 15 years generally take open source contributions as a very slight positive signal, but only one of many.