The symbols or "glyphs" are as follows:
Two intertwined threes, representing thirty
The hour and minute hand on a clock, representing seconds.
The three white lines form a introverted two, (the two lines in between the three) represent to.
And finially mars and it's moons represent mars.
So the symbols stand for Thirty Seconds To Mars.
Some people think the first symbol is Leto, however, as all the letters in their last name can be found in the first symbol.
However, as Jared has always been a fan of things such as these-heiroglyphics and whatnot, there is speculation as to whether or not Jared simply made these symbols up.
Other symbology of the band is their phoenix, representing eternal life and rebirth.
There is also "Provehito In Altum" (latin) the band's motto which translates to "Launch Forth Into The Deep"
There is also a symbol to represent this, a red arrow that is a visual version of Provehito in Altum
And there are four more symbols that are found on the booklet of the first CD, which we're not entirely sure the meaning of.
There is also the "X" which means dividing and multiplying, it also represents unity.
They also use the Skull or Trinity Seal and it represents power.
Hope this helps, and may I say, you've chosen an AMAZING band to gain interest in.
Most of this was just stuff I've learned being the huge fan I am, but this site might be helpful as well.