In this talk we are going to discuss an option-based mathematical indicator for stock price bubbles. The first introductory part recaps the strict local martingale theory for modelling asset price bubbles and its implications for pricing contingent claims. In the second part we present a novel forward-looking indicator based on the information content of bid and ask market quotes for exchange-traded plain vanilla options. Our construction is motivated by a recent theoretical result by A. Jacquier and M. Keller-Ressel proving that bubbles can be identified from the asymptotic behaviour of the implied volatility surface. However, in practice, the resulting inverse parameter identification problem is ill-posed and we adopt a statistical perspective in order to cope with this ill-posedness and to quantify the indicator’s inherent uncertainty. Finally, we provide real-market tests of the proposed indicator with focus on tech stocks addressing increasing concerns about a tech bubble 2.0.