I noticed this at Digital Point Forum. Only a minority of members are using post icons. A post icon can be used to give an idea about the type of your post when it is listed along with other posts. For an example, is your post about a question you have or is it about new finding or do you want to criticize something?

If post icons are available at your forum then you can use one of them at posting to give a better idea and to gain attraction. Most of vBulletin forums including Digital Point have this right under the post box as below,

Post Icons

Here is a screenshot I took of Digital Point forum home page. See how the question mark icon gives a better emphasis.

Post Icons at Home Page

Here is how the same post appeared at its category. You can notice that only a few posts contain icons.

Post Icons at Category Page