The easiest and surest way is to remove the left cup, and measure and/or thread guage it. That will tell you for sure whether the thread is 35x1 (French/Swiss) or 1.37x24 (BSC/ISO). If it's BSC life is easy, if it's 35x1, you have to toss a coin or do some trial and error removing the right cup to know the direction of threads.
Some brands use markings like rings turned into the face of the right cup to identify the direction of thread on French/Swiss cups. You might check a source like Sutherlands or possibly Sheldon Brown for some guidance there.
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