Hi igul talu
It seems unlikely that the hedgehog would have got mange in the shape of HI in capitals. So it seems most likely that someone has marked the hog. Not necessarily your neighbour, it might be someone who is trying to count how many hedgehogs they have visiting. Very sadly it is becoming more common for people to mark hedgehogs. Totally unnecessary and unkind to the hedgehogs. Not to mention the possibility of people thinking it’s a skin complaint or it even covering up a skin complaint.
However, if you are at all worried you can find the contact details of your nearest carer from the BHPS on 01584 890801. You can explain it to a carer in more detail and get the hog checked out if necessary.