FYI, letters to Ministers very, very, very rarely get seen by the Minister. They have people who deal with such things (my sis used to be one and another relative was a Minister). Your local MP is a slightly better bet (if they’re not a Minister) but even then they get masses of mail/e-mail and only a very select few will reach the target unless the subject is one of their personal hobby-horses.
County councils usually deal with roads and signage but beware wading through treacle. I used to have to deal with them professionally and it can be compared to digging heavy clay soil, huge amounts of effort with virtually no visible progress. It is however the place to start when trying to get road signs.
