Şırnak is a town in Southeastern Turkey. Be very careful about hitchhiking here as security is ultra tight with scores of military and police checkpoints everywhere because this is ground zero for the PKK. You will be repeatedly stopped, questioned, searched and registered and this normally takes 30 minutes to an hour. That being said they are always friendly and welcoming even if bewildered why you are there. (November 2017)
Hitchhiking out of Sirnak is likely to require some walking as the city is situated on a hill and all road pass around the hill. However atleast it's downhill all the way. Be cautius as locals are overly helpful and are very likely to take you to the busstation even though you clearly tell them (in turkish) what you want to do. One of the routes out marked on the map passes through a military zone, you will be detained and forbidden entry if you attempt to go through it. If you are going to Siirt then use the dirt road from the middle of the city.
Be careful with your hitchhiking hosts, my driver was detained with me for 2 hours as we crossed a checkpoint. They wouldn't let him go until they cleared me. (November 2017)
South towards Cizre
From the centre just follow the signs and walk down the hill on the serpentine road for about 2 kilometers until you get to a petrol station. From there you can easily flag down a ride to Cizre. If you do not want to walk, for 1 TL you can catch a bus that has a last stop precisely on that fuel station where you can start hitching directly. This bus goes frequently.
East towards Hakkari
This is, by far, the most militarized road in Turkey and there's a scarcity of vehicles. However the hitchhiker who perseveres and brings with him/her a fair amount of time and a whole lote of patience will be generously rewarded as this is (in hitchhiker Theo's modest opinion) the most scenic road in Turkey.
From the city centre you simply ask people for directions to Hakkari Yolu (there are almost no signs). Once you get to the Jandarma base you'll be able to see where the road from the city intersects with the 'ring road' which dont pass through Sirnak. There's a great hitchhiking spot about 50 meter after the intersection. Either walk the 2 kilometers there or try to hitch a ride.
You're likely to end up drinking tea with some soldiers as their bases are always located at intersections.
Update: it's currently a war there now so you're not likely allowed to enter the road.