Random nosebleeds = perverted thoughts is an old wive's tale from Japan, and is commonly depicted as a sight gag in anime/manga. However, while Rune Master does have anime and manga influences, it is a more Western/Indy-style comic, so I had to make the assumption not everyone would understand the noseblood gag, hence the footnote.
While we're on the subject of cultural things, for those of you who don't read the wiki
, here's a little more about what Duendo tattoos mean: The face tattoo represents their name, their torso tattoo their father's clan, and their limb tattoos their mother's clan. So, Diyero would have the same arm/leg tattoos as his mother, while his father would have the same torso tattoo, but they all would have different face tattoos.