January is one of the best months to hit the slopes in Europe, Canada, and the United States, but a keen contingent of skiers will nonetheless head for the salesroom at Christie’s London South Kensington branch to bid in person at the annual Christie’s Ski Sale. Scheduled for January 22, the auction will offer more than 200 iconic ski posters, most of them from the 1920s and ’30s, promoting some of the world’s most popular ski mountains and resorts. “It’s a very busy room,” says Nicolette Tomkinson, head of th…