An apparatus comprising: a hash table populator to: store hash keys representative of respective reference signatures included in a reference signature block associated with reference media in respective entries of a hash table in a database; and store qualifier data in an entry of the hash table corresponding to a hash key, the qualifier data including a timestamp, an offset, and an identifier associated with a reference signature represented by the hash key; and a block table populator to: store a block table key corresponding to the reference signature block in an entry of a block table in the database, the block table key including the timestamp and the identifier; and store the reference signature block, a preceding reference signature block of the reference media relative to the reference signature block and a subsequent reference signature block of the reference media relative to the reference signature block in the entry of the block table, the reference signature block being different than the preceding reference signature block and the subsequent reference signature block; and a signature matcher to access the hash table and the block table to retrieve candidate reference signatures to compare with site signatures representative of monitored media to identify the monitored media. a hash table populator to: store hash keys representative of respective reference signatures included in a reference signature block associated with reference media in respective entries of a hash table in a database; and store qualifier data in an entry of the hash table corresponding to a hash key, the qualifier data including a timestamp, an offset, and an identifier associated with a reference signature represented by the hash key; and store hash keys representative of respective reference signatures included in a reference signature block associated with reference media in respective entries of a hash table in a database; and store qualifier data in an entry of the hash table corresponding to a hash key, the qualifier data including a timestamp, an offset, and an identifier associated with a reference signature represented by the hash key; and a block table populator to: store a block table key corresponding to the reference signature block in an entry of a block table in the database, the block table key including the timestamp and the identifier; and store the reference signature block, a preceding reference signature block of the reference media relative to the reference signature block and a subsequent reference signature block of the reference media relative to the reference signature block in the entry of the block table, the reference signature block being different than the preceding reference signature block and the subsequent reference signature block; and store a block table key corresponding to the reference signature block in an entry of a block table in the database, the block table key including the timestamp and the identifier; and store the reference signature block, a preceding reference signature block of the reference media relative to the reference signature block and a subsequent reference signature block of the reference media relative to the reference signature block in the entry of the block table, the reference signature block being different than the preceding reference signature block and the subsequent reference signature block; and a signature matcher to access the hash table and the block table to retrieve candidate reference signatures to compare with site signatures representative of monitored media to identify the monitored media.