The Jonesy sign can be found during the third descent on the city tour mode map. Go down the first two slopes, then, when you go down the third slope, stick to the left wall. If you succeed, a wooden palisade will stop your fall and lead you into an alley on the left. Walk to the end of this alley and open the gate to find Jonesy's sign.
Written by Augustin "TheGreatReview" Héliot. Translated from French by Millenium.us.org.