Heres how you can pin/unpin and for even more help, heres why theres a pin on your dash. :)
How do I pin a post to the top of the Dashboard?
When creating a post, you can pin it by checking the “Promote this post” box and then selecting “Pin this post.” You can pin one post per day.
Why does a post at the top of my Dashboard have a red pin on it?
Pinned posts allow people you Follow to make sure you see important content. A pinned post will remain at the top of your Dashboard for 24 hours unless you click the little red pin at the top of the post.