Inspired by real ones put up after Ed Sheeran's 2017 song Castle On The Hill came under fire for containing the words "I'm on my way, driving at 90 down those country lanes".
http://www.telegraph.co.uk/news/2017/01/06/ed-sheeran-given-road-safety-advice-police-singing-driving-90/

Installation:

1: Extract the files to "C:\Program Files (x86)\Steam\steamapps\common\Grand Theft Auto V\x64h.rpf\levels\gta5\props\roadside\v_utility.rpf\"
N.B. Use Edit Mode

Inspiration:
http://www.bbc.co.uk/news/uk-england-suffolk-39128940