jinjur was the person who suggested it, and I believe she suggested it in four places (or at least, I put it in three of those places, and assume she mentioned the fourth.)

1) Journal profile
2) Fanlore editor profile
3) AO3 profile (or, presumably, all of the profiles for any fic archives which provide profiles; e-fiction archives typically have them)
4) And I assume on one's general website, although, since I yanked my fic from my website, I never added a permissions statement there.

And I just added it as the custom text box on my journal posting comm, so it'll appear on every story read there, so long as you keep my style.

I do not know if podficcers are actually looking for such statements or not. When I've spotted such statements in the wild (I don't usually do secondary fanwork, so I haven't gone looking) they've either been on people's journal profiles or their websites.