Communication source identifier verification system mechanisms are provided. The mechanisms receive communication information for a communication initiated between a source communication system and a destination communication system. The communication information comprises a source identifier and a local device identifier signature specifying zero or more local device identifiers of devices local to the source communication system. The mechanisms retrieve valid device identifier information for an authorized communication source corresponding to the identifier of the source communication system. The mechanisms execute a verification operation that verifies whether the source identifier is validly associated with the source communication system based on the retrieved valid device identifier information and the local device identifier signature. The mechanisms send a verification notification along with the communication information, in response to results of executing the verification operation, to the destination communication system.