The six signs do indeed "add up to" something suspicious. The Korean character in the flavortext is Unicode character CAFE (Unicode numbers being in hex); the key to the puzzle is to use the Unicode.
Adding the Unicode numbers of the letters in each sign gives another number which can be taken as Unicode for a letter. (In each case, that letter comes from an alphabet appropriate to the location.)
These unicode glyphs, when lined up and read upside down, read "VOWELS".