[YankForum]

you won't need to turn that on , that option is for inside posts , forcing html tags to compile , by certain groupds , and it's not secure to have it ON
the only thing you need to do is to edit one of these templates :

ad_showthread_firstpost_startstart
ad_thread_first_post_content
ad_thread_last_post_content
.....
postbit/postbit_legacy if you want the banner to appear after an specific post or even inside it
or maybe showthread template if you want the banner to appear in other places such as similar threads location and etc
you can even edit navbar and use an if condition to define limitations
etc