In Harry Potter 7, Harry visits his parent's graves. He also sees his old house, with a sign:
On this spot, on this night of 31 October 1981, Lily and James Potter lost their lives. Their son, Harry, remains the only wizard ever to have survived the Killing Curse. This house, invisible to Muggles, has been left in its ruined state as a monument to the Potters and as a reminder of the violence that tore apart their family.
The sign says the house is invisible to Muggles, therefore wizards can see it, such as the person who put up the sign, the people who scribbled on the sign, Hagrid who came to the site after the Potter's death, and Hermione who was beside Harry.
That doesn't make sense: We know Wormtail is the secret keeper and Wormtail isn't dead, and for all I know he didn't tell the whole wizarding world where the house was, so how can all the wizards see it?
