@Alula1 I'm not a fan of labels and post-it notes all over, I think it looks tacky. But you could make a graphically attractive note, in a small frame hung prominently on the kitchen wall, saying "Please be respectful and use only the cupboards designated for guest use, thank you." Since you greet them and point out what's available to them, they shouldn't need more than that reminder. You could put some cool, attractive stickers on the guest cupboards so they don't get confused.
If time allows, and you live onsite, I try not to overload guests with too much info when they first arrive- I'll show them where the lights switches are in their bedroom and bathroom, mention a few other things they need to know about those areas, then tell them I'll leave them to get settled and show them around the kitchen, etc, when they are ready. Guests are often tired from travelling when they arrive, may feel a bit disoriented in a new place, and just want to shower, unpack and relax on arrival. It's easier for them to absorb information when they've had a little wind-down.
For other areas than the kitchen, rather than Do Not Enter, a sign like "Private host area, no guest access" sounds more friendly.