One thing that helps cat and dog owners is for their animals to wear a collar to help identify them and to attatch a lead to in terms of a dog.

image wikipedia

So can guinea pigs wear collars at all?

Collars are not good for guinea pigs to wear. They are very comfortable for them and just not suitable for them to wear. They will find it quite distressing to wear them and will look to get it off.

If you must use something like this, then a harness is better and more comfortable for them. But personally I would not recommend putting anything on a guinea pig like this, it is just too cruel on them and would not do it to my piggies.