The number one counter mechanic to singed is somebody who doesn't have to chase him to punish him, and can punish him early and hard. Enter ranged, enter early, free, constant damage. Which just so happens to create teemo.
Unless it's proxy singed, then you need to lane swap and make your support harass singed and ward jungle entrances while your adc farms under turret, with jungle assisting top in the 2v1 bot and mid occaisionally coming around to fuck with singed. If you do it right and fast, it forces singed to play the conventional lane because he can no longer afford to proxy because he falls behind from the constant harass. It more effectively works with a ranged support, who almost always have spelltheifs, and it requires quick reactions to where singed is so the support can get some xp from lane when singed has backed to keep up with singed. It's in theory more effective than the jungle camps singed conventional reaction. Problem is that it's a team strat, so it doesn't work in soloq, which is why proxy singed is so goddamn stupid.