I reported your post to have it moved, but to answer your question, it's inconspicuous. I've mostly just bought a couple t-shirts and manga from the store, and every time I've gotten a padded envelope and it has Jacob's address - it doesn't say anything that would lead people to think it was adult material.
If you buy a book it's just going to feel like paperback books in there, or if you buy a DVD it's just going to feel like a DVD. Nobody but you will know what's in there.
Sidenote though, if you share a bank account keep in mind that FAKKU will show up on the bank statement.