/etc/logcheck/ignore.d.server/mon is in logcheck-database 1.3.16.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 3 | ^\w{3} [ :[:digit:]]{11} [._[:alnum:]-]+ mon\[[[:digit:]]+\]: authenticated monuser$
^\w{3} [ :[:digit:]]{11} [._[:alnum:]-]+ mon\[[[:digit:]]+\]: client command "(protid [[:digit:]]+|list (disabled|failures)|disable watch websites)"$
^\w{3} [ :[:digit:]]{11} [._[:alnum:]-]+ mon\[[[:digit:]]+\]: client connection from [.[:digit:]]+:[[:digit:]]+$
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