Hi Dumfriesman
You really need to contact your local highway authority. There do, apparently, exist official hedgehog signs, but from what I’ve heard it isn’t so easy to get permission to get one put up. I believe there are various regulations about the number of roadsigns in an area, visibility, road safety, etc. You never know, the fact that you already have a sign and they don’t have to pay for it, might make a difference!
Very sad that you found a dead hedgehog. That must have been distressing for you. The best thing you can do, to help the hogs avoid the need to cross roads, is to link as many gardens as possible with hedgehog highways. That way they will have access to more habitat without having the need to cross roads, or at least cross roads so often.
https://www.hedgehogstreet.org/help-hedgehogs/link-your-garden/
