Many business owners overlook strategically marketing to specific groups of people. Or in extreme cases, they just want to sell to EVERYBODY. The blanket approach can work, but it also wastes sweat equity and fungible funds.
You really need to figure out who your audience is going to be. Targeted marketing can save money because you're only reaching out to the people who already want a product or service like yours.
Be obvious, but not obnoxious with stickers. If the QR code is a scannable link to a menu, then put the sticker near the hostess booth or POS. If you own a rock climbing business, put the QR code sticker where it is highly visible so people standing in line can fill out the liability waiver while they wait.