For the average person working in tech, what's their most valuable credential?

I suspect for most it's the most "impressive job they've had, with a decay function for how long ago that was".

For me it’s the biggest impact on the team/product someone had

NFA. Dev/Artist. Exhibited Internationally.

/daily-art-mint
/daily-fan-token
/scanography
/cyanotype

How do you measure that besides having worked with them directly or an extremely credible but neutral backchannel reference

With great difficulty for sure unfortunately