They found that despite eBay's ban on ivory sales there were 183 ivory items on sale by 113 sellers during their research window between 18 January and 5 February 2017.

Not only did these sales violate eBay's trading conditions but some broke regulations under the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES) and EU regulations regarding the sale of 'unworked' ivory.

Despite the use of codes to hide sales and the problems this could pose law enforcement agencies working in different languages, the researchers found that the majority of items on offer -- around 80% -- were grouped around six code words across the four eBay sites monitored.

This suggests the sales of ivory items online between traders is standardising around set code words, even when using different languages, as globalisation and market forces affect their business like any other.

This could help narrow the scope within which law enforcement agencies have to search for the sale of ivory items and allow machine learning tools to be focused on key terms too, helping improve identification of illegal sales.

However, the researchers say further work will be required to monitor sites like Facebook, Twitter, Instagram and Craigslist to see what terms are used. These sites have different ways in which items are presented for sale and therefore it is not known to what extent these code words are not only shared between languages, but also across these online sales platforms.

Nonetheless, if a 'digital fingerprint' could be identified for the sale of ivory items or other wildlife trade items that spanned platforms, languages and countries, the global monitoring of wildlife trade could potentially be made easier.

Dr Roberts said: 'It is clear that identifying illegal online trade in ivory is a challenge for law enforcement agencies. However, the research shows that there are ways in which they can take advantage of market conditions that are forcing traders to standardise on code words to try and find buyers for their goods.'