"MARK" entries in /var/log/messages

[D. R. Evans]

When I look in /var/log/messages, I see a ton of lines that look like this:

Oct  4 18:37:27 homebrew -- MARK --
Oct  4 18:57:28 homebrew -- MARK --
Oct  4 19:17:28 homebrew -- MARK --
Oct  4 19:37:28 homebrew -- MARK --
Oct  4 19:57:28 homebrew -- MARK --
Oct  4 20:17:29 homebrew -- MARK --
Oct  4 20:37:29 homebrew -- MARK --
Oct  4 20:57:29 homebrew -- MARK --
Oct  4 21:17:29 homebrew -- MARK --
Oct  4 21:37:30 homebrew -- MARK --
Oct  4 21:57:30 homebrew -- MARK --
Oct  4 22:17:30 homebrew -- MARK --
Oct  4 22:37:30 homebrew -- MARK --
Oct  4 22:57:31 homebrew -- MARK --
Oct  4 23:17:31 homebrew -- MARK --
Oct  4 23:37:31 homebrew -- MARK --
Oct  4 23:57:31 homebrew -- MARK --
Oct  5 00:17:32 homebrew -- MARK --
Oct  5 00:37:32 homebrew -- MARK --
Oct  5 00:57:32 homebrew -- MARK --

What is causing these? They form by far the majority of the messages
in /var/log/messages, and they seem singularly useless.