Samsung Messages Bookmarks

[Enygma312]

Can anyone explain what that means in Samsung Messages? I've been wracking my brains trying to find the correct keywords are to describe that...but I think the screenshot is better. 

Is there a way to remove that? I don't remember ever bookmarking them..

It only happens with some messages from certain people and not with others. 

Help is appreciated.

[smbj_1005]

This appears as a reminder on top of the messages you have not read yet or maybe to separate your read messages from your unread ones. I think this happens automatically