1H, 2H, and 3H with the numbers being superscripts. H tells you it's hydrogen. The numbers how many particles in the nucleus - 1 proton, 1 proton and 1 neutron, and 1 proton and 2 neutrons for normal hydrogen, deuterium and tritium respectively.
Do a google search on isotopes of hydrogen. It's not like the information is hard to find.