Generally, law enforcement will only act on the trace once a formal police report has been filed in regard to the call.
Malicious caller identification, when subscribed or enabled, works by allowing a phone call recipient to mark or flag the preceding phone call connection as malicious (i.e. harassing, threatening, obscene, etc.).
To protect privacy the resulting trace data is only made available to law enforcement.
How the user activates this feature depends on their phone system – generally it is either in-band-signaling DTMF sequence such as the *57 Vertical service code or a special button attached to their phone generating an out-of-band signal.
Digital services, such as ISDN or GSM, enable the CPE to activate MCI via out-of-band signaling.