piefed has that and now it also has a neutral read icon that actually looks like a naught so delete but it basically marks it as read for people that choose the settings to not show read posts. This came up because they instituted a daily limit on voting. Before that I use to upvote everything to clear it from my feed when I refreshed. An interesting thing is with upvoting I did not do this but with the read button I suddenly realized with cat and owl and anim pictures and such I can not mark them read and then when I refresh they are in my feed to both let me know I caught up to where I was before and just make a nice little group of nice pictures to see.