Driven by technical innovation, embedded systems are becoming increasingly interconnected and have to be secured against failures and threats from the outside world. For this purpose, we have defined an integrated model-based development process for security monitors which requires an expressive, formally well-defined, and easy to learn behavioral signature language. In this paper, we demonstrate that Live Sequence Charts (LSCs) are adequate for the specification of behavioral signatures. To satisfy all requirements and enable compact modeling, we extend LSCs by concepts that fit well to the spirit of LSCs.