"Call this number if you need to move your car" only works if the number is easy to find and easy to dial correctly — which is exactly what a phone or SMS QR code solves better than printed digits.
Two options depending on urgency
For anything that needs an immediate response — someone's car is genuinely blocked — a phone QR code is better than SMS, because it gets you talking right away. For lower-urgency reports (a broken light, a maintenance request), an SMS QR code with a pre-filled message like "Reporting an issue at: " works well and doesn't demand an immediate call.
Weatherproofing matters more here than almost anywhere
Parking notices live outdoors permanently, not just for an event. A laminated sticker fades and peels within months; an engraved or UV-printed acrylic sign lasts years. If you're only budgeting for paper, plan to replace it every season.
Size for a quick glance while walking
People read parking signs while walking to their car, not standing still reading carefully. Go larger than you think you need — 6×6 cm minimum, more on a sign meant to be read from a few meters away.
Don't put personal information behind it
If the number goes straight to your personal phone, that's a real privacy tradeoff worth considering — a shared building line or a number you're comfortable being public is usually the better choice.