Light Yagami and L are often represented as opposites, even to the point that Light uses a PC and L uses an Apple Macintosh.
L, Misa, Light and his Father are seen in part 6 of "Full Metal Panic the 2nd Raid" outside the barber shop for about 3 seconds. "L" is riding a bicycle (right to left) and "Misa" is on the standing on the right, spying on Light and his father
The theme playing at the very beginning of the pilot is a chanted variation of the prayer Kyrie Eleison, which is Greek for "Lord have mercy."
When the police from around the world meet together at the Interpol meeting, most of the members there have a name tag with their names on it, and a flag to represent their country. It turns out that some of those name tags represent famous soccer players (real life players) from different countries, the name of the soccer player, being matched with the flag of the country which he is from.
When Naomi Misora's description if shown on the laptop at L's headquarters, you will notice that her description is made up of nothing but random letters strung together-- something that the Japanese audience would have most likely glazed over.