generally, the simplest way to determine the sex of a salamander, including tigers, is by observing their cloacal region, in males, espically during mating season, the males cloaca will appear to be slightly swollen, meaning they will have a swelling of the area right behind their hind legs at the base of the tail.
you should be cautious though and make sure that there is no unusual coloration, as well as swelling, such as red or marron on the underbelly of your salmander near the hind legs and tail, for this is a sign of redleg, a condition that is not common in salamanders, but is caused by a build up in toxins in the substrate. If this is witnessed, simply change the substrate.