The distinction is about what you're offering for sale, and it shows up in the wording and the audience.
Advertising the property means putting out something a member of the public would read as "this house is for sale by me," usually with photos, an address, a price, and no mention that you're a contract holder. That's the thing several states have folded into their definition of brokerage, since you'd be offering someone else's real estate to the public without a license. Nebraska and Kentucky both moved public marketing of a contract into brokerage territory, and the exact trigger differs by state, so this is a question for a local attorney rather than a rule you can carry across state lines.
Advertising the contract means what you're offering is your position as buyer. The pitch says you hold an executed purchase agreement on a property and you'll assign your rights in it for a fee. The disclosure is on the face of it. You still give the address and the condition and the photos, because a cash buyer can't evaluate anything otherwise. What changes is that the offer is the assignment, and the seller knows you're doing this because your contract says so.
So the address isn't the problem. The framing is, and so is who sees it. A private list of cash buyers who already know what you do sits very differently from a public listing site.
The piece people miss is that this only works if the seller genuinely agreed to it in writing. If your seller signs a contract with an assignment clause buried in paragraph fourteen and later says nobody explained it, your careful marketing language won't save you.
