This is an interesting subject... verbal permission used to be enough in the early days, but now in the internet era, simply posting an image online creates a level of public exposure almost if not greater than having that image published. Privacy has become a big issue. I can understand why the law is there.
But this can be a dilemma for those of us that take re-creational photos in public. Here's what I'm aware of (might be different in your area).
As I understand it, taking a photo of a public figure is ok (actors, dancers, performers, athletes, politicians, etc) but only while they are in the context of a public event. If we photograph a crowd in general in a public place, with no one standing out in particular - it should be OK. However, if a stranger is the main subject especially in close-up or telephoto compositions, it pays to get permission - even after the photo had already been taken (but preferably before). Of course we need to be prepared to delete the photo in front of them should permission be denied. Taking photos inside a private area (even from a public stand point) is a very different matter altogether and may incur penalties depending on various local laws.
Signing is a problem area as well. The signature is only as good as the document it's written on. A disclaimer or model release form is less intimidating if it is written with as much ordinary language as possible (avoid legal terms), but must first be checked and approved by a lawyer well versed in these matters - otherwise the signature may be invalid. In some instances, a signature of release only applies to the person giving permission, but heirs/relatives/clans/tribes may still be able to lay claim to certain rights of ownership as facial features may have direct genealogical implications on them. This may have to be addressed in the document. Even if the subject is happy and willing to have their face photographed, it still pays to acquire permission correctly.
The key in all of this is respect. If everything is done respectfully (including the theme of the photo composition itself), then seeking approval shouldn't be a hassle. A compliment or a commendation might even come our way.