Yes, I believe some rescues do mark the hogs before release, but hopefully they would follow BHPS suggestions:
“Can I ‘mark’ my hedgehogs?
We’re pretty sure a hedgehog would rather not be marked, but if you are going to do it, please do ensure that you use a non-toxic water-based marker and mark just a few spines of the hedgehog. Keep the mark away from the hedgehog’s face and mark it in the garden on the ground rather than picking it up/bringing it indoors. Please don’t use red as people may mistake it for blood and ‘rescue’ it. Do not make hedgehog conspicuous to predators. We have seen some very sad images of poor hedgehogs practically covered in paint! If you are watching the hedgehogs on a wildlife camera you will often be able to tell them apart over time without the need for marking.”
It’s good to hear you have had a few hogs visiting. Some hogs decide to stay out and about all winter, but they may decide to hibernate now we have this frosty weather – not so easy to dig up worms when the ground is so hard!
If hogs are still around, it’s important to make sure they have food and water available. Dry cat food is probably best in this weather, as wet cat/dog food would be likely to freeze. Water sometimes stays unfrozen if you put it in a wooden hog feeding box or put it in a sheltered place close to a house. But puttting more water out last thing at night at least gives the hogs a chance to access some.
Good luck to you and the hogs.