SAN FRANCISCO — Lawyers for smaller companies have been known to accuse Google Inc. of stealing and profiting from their clients’ trade secrets. But this time, the slighted company’s lawyers say Google left behind a paper trail of Post-its as evidence.

London-based VSL Communications has accused Google of stealing its novel method for shrinking video and audio files without sacrificing image or sound quality. Google used those trade secrets to enhance the streaming and downloading features of virtually all Google services, including YouTube, Google Play and Google Earth, according to the complaint filed Monday in Santa Clara County Superior Court.