sign, symbol, mark

(ひょうしき) ”Marked”, as in ‘obey the rules which have been posted on the wall’. ‘follow the marked trail’, ‘Follow the target kitty which has been tagged with a blue collar’
(きごう) One of the weird squiggles used in codes. Also a specialty sign – like musical notation or chemical notation. Not a language per se, but a symbol used by a scientist or specialist. Also, an algebraic sign:“Let’s call the diameter of the circle X,” said the Professor, scribbling at the chalkboard. In that case, the X is a きごう。
(しょうちょう) Literary symbol:“In the novel, the trees symbolize life.” ‘The color red in the painting symbolizes communism.’
(しるし) A symbol, a logo, a crucifix, a skull-and-crossbones.   $$$
(ふごう) Basically it’s any kind of visual communication besides voice and ‘regular’ letters – Morse code, binary code, semaphore code. Also it can mean a hieroglyph or ideograph (old Chinese letters that are more like pictures), or a punctuation mark.
(あんごう) Secret spy codes, encryption.