Jared Leto has 2 tattoos.
This is an idea of what the long one could mean:
₪ The first symbol is two intertwined "M's" which could stand for Mercury.
o The second symbol looks like it is rotating in the opposite direction and Venus rotates in the opposite direction of all the terrestrial planets.
III The third symbol is the roman numeral three which stands for Earth, the third planet from the sun.
.o• The fourth symbol is Mars. The two dots represent both of Mars's moons Phobos an Deimos.
The second explination is that they stand for the bands (30 second to mars) name:
₪ The first symbol is two intertwined threes representing 30.
o The second symbol is rotating in the opposite direction, almost as if it is counting down which symbolizes seconds.
III The third symbol is three vertical lines, but if you look in between them you get the roman numeral two which stands for to.
.o• The last symbol represents Mars once again, with its two moons Phobos and Deimos.