The program has two separate "post acknowledgement" features.
One is adding to member reputation. To add to a member's reputation, click on the badge or six pointed star under the member's name. This will allow you to send a comment to the member letting them know you added to their reputation and why. It is not mandatory you enter a comment to add to a member's reputation.
The other way to add to a member's reputation is to click on "Nominate this post for special consideration". This option should be selected after you are to add to a member's reputation and does not provide the option to add a comment as to why you nominated the post.
If you click on "Nominate this post for special consideration" before clicking on the badge, the program will not allow you to add to the member's reputation or make a comment.
Step by step....
1. click on the badge under the member's name
2. add comment
3. click on nominate post (if you think the post is worthy of special consideration)
Eventually, all of the nominated posts will be stuck at the top of their respective forums.