I travel a fair bit for work (and pleasure), and have noticed recently how road signs have become increasingly hidden by trees.    I often find myself concentrating on trying to read the signs only to find that I am either in the wrong lane and it's too late to change, or worse still, I am travelling in the wrong direction   It is something that really annoys me and I am not sure who's resposibility it is to ensure they are not obscured and thereore, who I should complain to                                                                                                                                                                              

Most signs are local council, but major routes are covered by Highways Agency. The HA do a relatively good job with theirs, so it's probably going to be council ones.
                                                                                                                                                                              

Likely to be local council. Bet they don't have this problem with speed scameras.