WE trust the organisers of the Art For Safer Sex exhibition which opens on Friday at Times Square are aware of what they might have let themselves in for. For in their wisdom they have invited two of the most outrageous characters in our restrained little town to lend their creative talents to the cause. Zany caricaturist Bill Yim and multi-media sage Greenstreet Kan are Hong Kong's answer to New York's shock-jocks - only in their case they do their worst behind a drawing board rather then a studio mike. Yim and Kan live to outrage - and they tackle that mission with lascivious zeal. The Christmas card which Yim sends out to his friends ('This year it goes beyond all bounds of decency and will be more disgusting than ever,' he says gleefully) has attained cult status, and each year succeeds in turning the blushes of the recipients redder than Santa's briefs. And Kan's most recent literary offering was an explicitly illustrated sex therapy book that made the Kama Sutra look like a Sunday school manual. Yim's idea of safe sex is characteristically summed-up in the title of one of the three cartoons - Sex with a bamboo tree - that he told Keeping Posted he is contributing to the exhibition. We understand that Kan will be contributing what he prefers to merely refer to for the moment as a 'suitable calligraphy'. But rumour is that he has drawn inspiration from Emperor Caligula's Rome - although history, as seen through the eyes of Hollywood, records that safe sex was the one thing Caligula never practised. But whatever it might be that Yim and Kan choose to exhibit, we can rest easy in the sure knowledge that the moral police will be first in the queue when the show opens.