How to suppress the "Current Location" callout in map view

There's a property on the annotation view you can change, once the user location has been updated:

- (void)mapView:(MKMapView *)mapView didUpdateUserLocation:(MKUserLocation *)userLocation
{
    MKAnnotationView *userLocationView = [mapView viewForAnnotation:userLocation];   
    userLocationView.canShowCallout = NO;
}    

Swift 4

// MARK: - MKMapViewDelegate

func mapViewDidFinishLoadingMap(_ mapView: MKMapView) {
    if let userLocationView = mapView.view(for: mapView.userLocation) {
        userLocationView.canShowCallout = false
    }
}

Swift 4 - Xcode 9.2 - iOS 11.2

// MARK: - MKMapViewDelegate

func mapView(_ mapView: MKMapView, viewFor annotation: MKAnnotation) -> MKAnnotationView? {
  if let userLocation = annotation as? MKUserLocation {
    userLocation.title = ""
    return nil
  }
  // ...
}

You can set the title to blank to suppress the callout:

mapView.userLocation.title = @"";

Edit:
A more reliable way might be to blank the title in the didUpdateUserLocation delegate method:

-(void)mapView:(MKMapView *)mapView didUpdateUserLocation:(MKUserLocation *)userLocation
{
    userLocation.title = @"";
}

or in viewForAnnotation:

- (MKAnnotationView *)mapView:(MKMapView *)mapView viewForAnnotation:(id<MKAnnotation>) annotation
{
    if ([annotation isKindOfClass:[MKUserLocation class]])
    {
        ((MKUserLocation *)annotation).title = @"";
        return nil;
    }

    ...
}

Setting the title in the delegate methods lets you be certain you have a real userLocation instance to work with.