One can view the position of Mars for a specific date and time on the Mars24 plots by using the Settings tool found in the Window drop down menu. The orbit and analemma plots for perihelion are shown below. Ls in the analemma plot appears to be the Sun's RA given in degrees of longitude and is used in place of a date.
Supplemental (Nov 19): The Mars24 technical notes state that Ls is the areocentric longitude of the Sun measured from the Martian equinox. This is probably the relative longitude along the celestial great circle of the Martian ecliptic due to the Sun's motion in its "areocentric orbit." Ls is also used in connection with the ephemeris time (ET).