These are called monument signs or ground signs. For a long time, there was only an advertising=totem tag for a pole sign or pylon sign, and only if it was being used to advertise a business. However, a recent discussion about signs with a political message resulted in a new man_made=sign tag that isn’t limited to a particular form factor or message. To indicate that the monument sign isn’t supported by a pole, you could try support=ground/pedestal or location=surface.