The ad agencies using their creativity to highlight slavery, poverty and conflict this holiday season

For most of the year, advertising agencies shout about their awards, new clients or star hires. But when the holiday season comes around, they use their creativity for good causes.

Images of slavery might not be something normally associated with Christmas, but London ad agency Aesop has used them to illustrate classic decorations – paper chains – to highlight the fact that there are up to 13,000 victims of modern slavery in the U.K. today.

They tell the stories of three refugees who came to the U.K. for asylum but instead ended up as "modern" slaves. The paper chains show Christmas imagery such as snowflakes, holly and gifts with the stories of a sex-worker, an underpaid restaurant hand and a girl whose aunt tried to drown her in a bath.

Charity Unseen is selling the paper chains via its website and chief executive Andrew Wallis said in a statement: "Often this crime and the exploitation of people is hidden in plain sight and the psychological chains that hold people in situations of modern slavery are very real."

Grey Canada and the Salvation Army

Hidden suffering is also used as a theme by the Salvation Army in Canada this festive season, in ads created by Grey Canada. The trend for family portraits to feature on Christmas cards is used in video and print ads to highlight the fact that behind their smiling faces may be a life of poverty.

The "Poverty isn't always easy to see" campaign started earlier this year, and the current ads call for donations over the holidays.

M&C Saatchi Abel and Stamps For Good

M&C Saatchi Abel's Stamps for Good initiative supports causes including Habitat for Humanity SA
M&C Saatchi Abel's Stamps for Good initiative supports causes including Habitat for Humanity SA

Meanwhile, South African agency M&C Saatchi Abel has designed clickable charity postage stamps that people can attach to their email signature when their employer signs up to agency's Stamps For Good initiative.

Employers donate to one of ten charities, represented by the postage stamps, and the aim is to use the emails to spread the word to other businesses and encourage them to be part of the scheme.

Proximity London and Evelina London Children’s Hospital

Ad agency Proximity London is giving gifts to the Evelina children's hospital
Ad agency Proximity London is giving gifts to the Evelina children's hospital

Proximity London has used the popularity of the emoji to raise money for children's hospital Evelina. Friends of the agency have been asked to tweet the symbols to the Twitter handle @EmojiUpAGift, and corresponding presents are being sent to the hospital. It has sent 100 gifts to children there.

McCann London and Doctors of the World

Conflict in the Middle East is the subject of Christmas cards from Doctors of the World. They blend Press Association photography with illustration showing traditional scenes from the Nativity on cards designed for free by agency McCann London, including Joseph leading Mary on a donkey through a war-torn city and the couple bending over Jesus in front of a rocket being launched in the night sky.

UK agencies and ChristmasSOwhite

Helen Marsden | ChristmasSOwhite

Eight U.K. agencies are supporting ChristmasSOwhite, which is aimed at protesting "the under-representation of people of color online with particular focus on Christmas."

Founder Nadya Powell set up the initiative after a school Christmas fair, where she had a stall where children could create their own festive websites, and found that every image searched for only showed white families.

ChristmasSOwhite set up a photo shoot to celebrate diversity and represent the "unseen Christmas experience," and is encouraging people to tweet and email pictures to the campaign.

Follow CNBC International on Twitter and Facebook.