Jan Egesborg and Pia Bertelsen, who call themselves "Surrend", short for surrender, are in Belgrade where posters of Mladic and Vojislav Kostunica, the Serb prime minister, have been plastered by nationalist groups, in public places.
Posters of Mladic are now covered with green stickers with the text in Serbian stating "We know where you are - surrend", "We know where you hide - surrend" and "We know you have fragile nerves - surrend".
Bertelsen, 32, says "we don't want to cause hate or anger with these stickers.
"All we're trying to mainly do is make people stop and think and maybe laugh a bit, but make up their own minds."
Serbia promised to hand over Mladic to the international war crimes tribunal in The Hague by the end of April.
The court has charged Mladic with genocide and other crimes against humanity - including the massacre of about 8,000 Muslim men and boys from Srebrenica in 1995. Mladic has remained at large for more than 10 years.
The EU called off talks on closer ties with Serbia when it failed to meet the deadline.
Nationalist groups have plastered
posters of Mladic across Belgrade
"Kostunica has risked the future of the country," says Bertelsen, who together with her fellow street artist, also covered posters of Kostunica with stickers, in Serbian, stating "We know you are a coward".
"We think Kostunica is a coward because he did not keep his promise," she adds.
This is the third time the duo is in Belgrade with their "weapons".
The first was for the funeral of Slobodon Milosevic and the second late in April to highlight that Mladic's time was up.
"There have been varied responses to our protest," says Bertelsen.
"People stop to look at the posters. Some are smiling. Some thinking. Of course, there are some who shake their heads and think it's in bad taste."
"People stop to look at the posters. Some are smiling. Some thinking. Of course, there are some who shake their heads and think it's in bad taste"
"But mostly, we get the impression that people are saying, 'It's okay that you're doing it'", added Bertelsen.
Bertelsen says the aim of Surrend is to take art to hotspots.
Her colleague, Egesborg, 42, and another artist, Claude Rohland, had put up anti-war posters in Baghdad last year.
In Zimbabwe, they placed advertisments in newspapers, "making fun of" Robert Mugabe, the country's president.