Thrust is a reaction force so it is the direction it makes the turbine go is the way it is pointed, so if the turbine is pointed up (starter at the top) it is up thrust, and if pointed down, it is down thrust, simple as that. Think on it as a firework or rocket.

Seems to be a lot of confusion over this and discussed many times on forums before, if your prop engine is at the front and the engine is pointing down then everyone knows this as down thrust, as it is now being pushed at a downward angle by the thrust, forget for now that it is bolted to an aeroplane.
It is the exact same with a turbine, think of the air coming out of the back, being the same as the air coming out of the back of a prop, replace the engine with a turbine with the same angled down mount and you have the same thing.

NOTE
Up thrust is always UP thrust, and DOWN thrust is always DOWN thrust no matter where it is mounted on an aeroplane.

What an aircraft needs to trim it for normal straight flight will depend on the aircraft design. Engines, we will call them thrust/push producers mounted at the back can react differently when behind the CG and whether the thrust produced exists above or below the tailplane. (benoli effect)
In general it is found for thrust producers mounted on the front of an aircraft the trust direction is down and on the rear of an aircraft the thrust direction is UP. The thrust producer may be seen to be angled down at the back but the thrust it produces is UP. What this then does to an aircraft is a different matter and may cause it to pitch down which is where the confusion lies.

On many twin boom aircraft fitted with a turbine, in order to keep the hot gases away from the tailplane the exhaust is angled down but may have no effect at all to the trim of the aircraft.
I found by increasing this rear UP thrust (exhaust angled further down) my Bobcat (not bvm) would now fly off the runway on its own where as before with the turbine level it needed to be hauled off and used to jump into the air.