A good indicator of a bubble in SF/SV startups is measuring the IT job market using local Craiglist and Dice job postings since startups heavily use them.

I used both websites on & off since the late 90s to find contract & permanent full-time jobs. Back then at the height of the dot-coms, the Dice home page showed 120,000+ jobs, right after the crash (2001-2003) that number fell to around 20,000-30,000. Now it's around 80,000.

On Craigslist, at the dot com height, the Software section for the Bay Area (https://sfbay.craigslist.org/search/sof) had so many job postings per day that the list of postings for that day would spill over to the next page (there are 100 listings per page). A year & a half ago (late 2014) there was a good amount of postings and I got a frenzy of replies when I contacted them. Now, there's only a handful of postings per day.