Symbol against a group of messages in Forte Agent

Means "Ignore sub thread" "One of the key features of Agent is it's ability to thread messages, that is, to show responses to messages indented beneath the original message. Some messages threads can have a great many messages, with offshoot discussions in which you are not interested cropping up in "subthreads". In this case you want to find the top message of such a discussion and ignore it and all the responses to it, while not ignoring other threads in the message. In Agent you do this by using the Ignore command on the top message in those subthreads you don't want to read. Agent will mark this message and all messages in the thread below this message read, so you can ignore them."

Same at ALT + K in thunderbird: kill sub thread

Thanks. Little symbol cleared.

...

And an easy way to invoke the command is to press the "i" key. Pressing again on an ignored subthread clears the marker. I usually blame the cat for these keyboard oddities.