I think you can tell the difference from whether you have 1 or -1 in the Z line (or column depending on the matrix orientation). In particular:
- Left handed: 1
- Right handed: -1
For a comparison, see both of these links - D3DXMatrixPerspectiveLH and D3DXMatrixPerspectiveRH. Since DirectX is left handed, you'd normally use the left handed version which has a 1 in the third row fourth column.
On the other hand, OpenGL and XNA are both right handed and I can confirm that the perspective matrices they generate use -1 instead, although OpenGL has it in the fourth row third column, whereas XNA has it in the third row fourth column like DirectX (column major matrices versus row major matrices).