This paper provides an introduction to and discussion of SIGNAL, an industry-scale process data querying language and engine for large-scale cloud-based systems that is developed by SAP Signavio. SIGNAL is optimized for fast read access to process data in event log format and utilizes an in-memory columnar store to this end. To facilitate usability, SIGNAL uses an SQL-like syntax with additional domain-specific querying features and in particular row-pattern matching-based temporal operators. Also, the paper highlights research challenges related to process querying that are informed by the implementation and application of SIGNAL.