Suppose that 

means $a+b-c$.
For example, 

is $5+4-6 = 3$.
Then the sum 

is
$\text{(A)}\ -2 \qquad \text{(B)}\ -1 \qquad \text{(C)}\ 0 \qquad \text{(D)}\ 1 \qquad \text{(E)}\ 2$
The first triangle represents $1+3-4$
The 2nd triangle represents $2+5-6$
Solving the first triangle, we get $0$
Solving the 2nd triangle, we get $1$
Since we have to add the 2 triangles the final answer is $1$, which is $\boxed{D}$.