like you would any L mod. feel the edge of the rim. if there is a notch, it is an X mold, if it is smooth, it is an L mod.
discs that have L mods:
Eagle (unmarked, all new will be EL)
Teebird (pro TL, star TL)
Firebird (unmarked, pro FL)
Starfire (unmarked, pro SL, star SL, about 15% of champ)
Monster (unmarked, all new champ will be ML)