Show affiliate disclaimer only on certain posts

Hello,

I am trying to neatly add an affiliate link disclosure to my posts, for example below the byline.

However, most of my posts do not contain affiliate links and I only want to display this disclaimer on the posts that do.

Is it possible to add some kind of checkmark or custom field to the post editor screen. Then make the disclosure only show when that is checked?

So if the affiliate disclosure is enabled in the posts, then it shows the disclosure below the byline.

Thanks,
Kristjan